記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.35848/1347-4065/acf2a3

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Wiley  

DOI： 10.1002/aelm.202201303

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/adfm.202213144

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society ({APS})  

DOI： 10.1103/physrevb.107.l041201

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0115384

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society ({ACS})  

DOI： 10.1021/acs.inorgchem.2c00604

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

Tin mono-selenide (SnSe) exhibits the world record of thermoelectric conversion efficiency ZT in the single crystal form, but the performance of polycrystalline SnSe is restricted by low electronic conductivity (sigma) and high thermal conductivity (kappa), compared to those of the single crystal. Here an effective strategy to achieve high sigma and low kappa simultaneously is reported on p-type polycrystalline SnSe with isovalent Te ion substitution. The nonequilibrium Sn(Se1-xTex) solid solution bulks with x up to 0.4 are synthesized by the two-step process composed of high-temperature solid-state reaction and rapid thermal quenching. The Te ion substitution in SnSe realizes high sigma due to the 10(3)-times increase in hole carrier concentration and effectively reduced lattice kappa less than one-third at room temperature. The large-size Te ion in Sn(Se1-xTex) forms weak Sn-Te bonds, leading to the high-density formation of hole-donating Sn vacancies and the reduced phonon frequency and enhanced phonon scattering. This result-doping of large-size ions beyond the equilibrium limit-proposes a new idea for carrier doping and controlling thermal properties to enhance the ZT of polycrystalline SnSe.

DOI： 10.1002/advs.202105958

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society ({ACS})  

DOI： 10.1021/acsami.2c01464

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing Ltd  

The relationship between the magnetic interaction and photoinduced dynamics in antiferromagnetic perovskites is investigated in this study. In La1/3Sr2/3FeO3 thin films, commensurate spin ordering is accompanied by charge disproportionation, whereas SrFeO3-delta thin films show incommensurate helical antiferromagnetic spin ordering due to increased ferromagnetic coupling compared to La1/3Sr2/3FeO3. To understand the photoinduced spin dynamics in these materials, we investigate the spin ordering through time-resolved resonant soft x-ray scattering. In La1/3Sr2/3FeO3, ultrafast quenching of the magnetic ordering within 130 fs through a nonthermal process is observed, triggered by charge transfer between the Fe atoms. We compare this to the photoinduced dynamics of the helical magnetic ordering of SrFeO3-delta . We find that the change in the magnetic coupling through optically induced charge transfer can offer an even more efficient channel for spin-order manipulation.

DOI： 10.1088/1367-2630/ac5f31

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI LTD  

The development of p-type oxide semiconductors is challenging owing to the localized nature of the valence band maximum (VBM), which primarily comprises O 2p orbitals. Although some Sn2+-based pyrochlore-type oxides (A2B2O7) with VBMs comprising spatially spread Sn 5s orbitals show p-type semiconducting properties, these properties cannot be tuned by an intentional chemical doping owing to the instability of their valence states. Herein, the influence of chemical doping on the crystal structure and electrical properties of Bi2Sn2O7, whose VBM is composed of valence-stable ions with Bi 6s orbitals, in the VBM is investigated. X-ray absorption spectroscopy reveals that In3+ is doped substitutionally at the Sn4+ site. Although the doped In3+ ions are expected to act as acceptors, their electrical properties always show n-type character. Simultaneously, extended X-ray absorption fine structure reveals the formation of oxygen vacancies in Bi-O-Bi bonds contributing to the VBM, whereas negligible changes are observed in the SnO6 octahedra, suggesting that the generated holes are electrically compensated by electrons because of the oxygen vacancies. P-type electric properties can be observed under oxidizing conditions, providing a critical design concept for the realization of hole conduction in acceptor-doped Bi2Sn2O7. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

DOI： 10.1016/j.matdes.2022.110549

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

Dynamic control of thermal transport in solid materials is highly desired for thermal management technology. However, the development of a material exhibiting large modulation of thermal conductivity (kappa) by external stimuli remains a major challenge. Here, the large kappa modulation is reported by the reversible 3D to 2D crystal structure transition in a nonequilibrium solid solution of (Pb1-xSnx)Se, where Pb2+ stabilizes a 3D cubic structure while Sn2+ does a 2D layered structure. The phase boundary of these phases is induced in (Pb0.5Sn0.5)Se bulk polycrystals by thermally quenching the high-temperature solid solution phase. Through the 3D-2D phase transition, the 1/2.9-times decrease of lattice kappa (kappa(lat.)) is achieved by strong phonon scattering in the 2D layered structure, and the electronic kappa (kappa(ele.)) is also decreased by 5 orders of magnitude due to the electronic phase transition from a 3D high conductivity state to a 2D semiconducting state. The total kappa (=kappa(lat.) + kappa(ele.)) modulation ratio kappa(3D phase)/kappa(2D phase) = 3.6 is attained at 373 K. The present strategy will lead to a novel concept for designing thermal management materials through crystal-structure dimensionality switch using nonequilibrium phase boundaries.

DOI： 10.1002/aelm.202200024

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Royal Society of Chemistry ({RSC})  

<jats:p>The development of p-type oxide semiconductors has shown promise in overcoming limitations restricting the practical usage of oxide semiconductors and the realization of innovative functional devices. Through numerous studies based...</jats:p>

DOI： 10.1039/d2ma00815g

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acsaelm.2c00181

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

Introducing artificial strain in epitaxial thin films is an effective strategy to alter electronic structures of transition metal oxides (TMOs) and to induce novel phenomena and functionalities not realized in bulk crystals. This study reports a breaking of the conventional trade-off relation in thermopower (S)-conductivity (sigma) and demonstrates a 2 orders of magnitude enhancement of power factor (PF) in compressively strained LaTiO3 (LTO) films. By varying substrates and reducing film thickness down to 4 nm, the out-of-plane to the in-plane lattice parameter ratio is controlled from 0.992 (tensile strain) to 1.034 (compressive strain). This tuning induces the electronic structure change from a Mott insulator to a metal and leads to a 10(3)-fold increase in sigma up to 2920 S cm(-1). Concomitantly, the sign of S inverts from positive to negative, and both sigma and S increase and break the trade-off relation between them in the n-type region. As a result, the PF (=S-2 sigma) is significantly enhanced to 300 mu W m(-)(1)K(-2), which is 10(2) times larger than that of bulk LTO. Present results propose epitaxial strain as a means to finely tune strongly correlated TMOs close to their Mott transition, and thus to harness the hidden large thermoelectric PF.

DOI： 10.1002/advs.202102097

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

An unusually large thermopower (S) enhancement is induced by heterostructuring thin films of the strongly correlated electron oxide LaNiO3. The phonon-drag effect, which is not observed in bulk LaNiO3, enhances S for thin films compressively strained by LaAlO3 substrates. By a reduction in the layer thickness down to three unit cells and subsequent LaAlO3 surface termination, a 10 times S enhancement over the bulk value is observed due to large phonon drag S (S-g), and the Sg contribution to the total S occurs over a much wider temperature range up to 220 K. The S-g enhancement originates from the coupling of lattice vibration to the d electrons with large effective mass in the compressively strained ultrathin LaNiO3, and the electron-phonon interaction is largely enhanced by the phonon leakage from the LaAlO3 substrate and the capping layer. The transition-metal oxide heterostructures emerge as a new playground to manipulate electronic and phononic properties in the quest for high-performance thermoelectrics.

DOI： 10.1021/acs.nanolett.1c03143

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

A layered semiconductor, SrTiN2, has an interesting crystal structure as a two-dimensional (2D) electron system embedded in a three-dimensional bulk periodic structure because it has alternate stacking of a SrN blocking layer and a TiN conduction layer, in which the Ti 3d(xy) orbital forms the conduction band minimum (CBM) similar to the SrTiO3-based thin-film heterostructure. However, SrTiN2 has been reported to exhibit nearly degenerate conduction, but we reported that it would be due to the easy formation of nitrogen vacancies and oxygen impurities from air. In this paper, we extend the materials to family compounds, alkaline earth (AE) ion-substituted, AETiN(2) (AE = Ca, Sr, and Ba), and investigated how we can suppress the defect formation by (hybrid) density functional theory calculations. All AETiN(2) compounds possess thermodynamic stability in the wide nitrogen (N) chemical potential window. Especially, CaTiN2 is the most stable even against N-poor conditions. Unintentional carrier generation occurs due to the nitrogen vacancies (VN), oxygen substitution (ON), and hydrogen anion substitution (HN) at the nitrogen sites. The V-N and H-N impurities can be suppressed under N-moderate and N-rich conditions. The ON defect is easily formed in SrTiN2 and also in BaTiN2 under N-rich conditions, but its formation can be suppressed in CaTiN2. Present results suggest that high-purity CaTiN2 can be obtained under wider N chemical conditions, which would lead to the realization of the novel functional properties originating from Ti 3d(xy) 2D bands embedded in the bulk crystal structure.

DOI： 10.1021/acs.inorgchem.1c00526

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcc.1c02437

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/5.0044047

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Association for the Advancement of Science (AAAS)  

Material properties depend largely on the dimensionality of the crystal structures and the associated electronic structures. If the crystal-structure dimensionality can be switched reversibly in the same material, then a drastic property change may be controllable. Here, we propose a design route for a direct three-dimensional (3D) to 2D structural phase transition, demonstrating an example in (Pb_{1−<italic>x</italic>}Sn<italic>_x</italic>)Se alloy system, where Pb²⁺ and Sn²⁺ have similar <italic>n</italic>s² pseudo-closed shell configurations, but the former stabilizes the 3D rock-salt-type structure while the latter a 2D layered structure. However, this system has no direct phase boundary between these crystal structures under thermal equilibrium. We succeeded in inducing the direct 3D-2D structural phase transition in (Pb_{1−<italic>x</italic>}Sn<italic>_x</italic>)Se alloy epitaxial films by using a nonequilibrium growth technique. Reversible giant electronic property change was attained at <italic>x</italic> ~ 0.5 originating in the abrupt band structure switch from gapless Dirac-like state to semiconducting state.

DOI： 10.1126/sciadv.abf2725

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Tin mono-selenide (SnSe) is one of the most promising thermoelectric materials; however, it experiences difficulty in controlling the carrier polarity, which is inevitable for realizing p-n homojunction devices. Herein, double switching of charge polarity in (Sn1-xSbx)Se by varying x is reported; pure SnSe shows p-type conduction, whereas the polarity of (Sn1-xSbx)Se switches to n-type conduction for 0.005 < x < 0.05, and then re-switches to p-type conduction for x > 0.05. The major Sb substitution site switches from the Se (Sb-Se) to Sn site (Sb-Sn) with increasing x. Sb-Sn (Sb3+ at Sn2+) works as a donor, but Sb-Se (Sb3- at Se2-) does not produce a hole because of the Sb-Sb dimer formation. The mechanism of double polarity switching is explained by native p-type conduction in pure SnSe due to Sn-vacancy formation, whereas (Sn1-xSbx)Se exhibits n-type behavior due to conduction through the Sb-Se impurity band formed above the valence band maximum, and finally re-switches to weak p-type, where the Fermi level approaches the midgap level between the Sb-Se band and conduction band minimum. Clarification of the Sb doping mechanism will provide a crucial guide for developing more sophisticated doping routes for SnSe and high-performance energy-related devices.

DOI： 10.1002/adfm.202008092

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：John Wiley and Sons Inc  

Amorphous oxide semiconductors (AOSs) have been widely applied for state-of-the-art flat-panel display as a thin-film transistor (TFT) since 2012. Besides, AOSs have been studied not only for TFT but also for other electronic devices such as sensor, diode, transport layer, memory, and so on. To realize those next-generation electronics using AOS material, it is important to understand the defect state in AOS material. Here we review research about defects in AOS up to now including O-related, hydrogen-related, and structure-related defects, which are important to understand the AOS feature. At the conference, we will also mention the exploration of new functional AOS materials based on defect engineering.

DOI： 10.1002/sdtp.14389

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

GeO2 has an a-quartz-type crystal structure with a very wide fundamental band gap of 6.6 eV and is a good insulator. Here, we find that the stable rutile-GeO2 polymorph with a 4.6 eV band gap has a surprisingly low similar to 6.8 eV ionization potential, as predicted from the band alignment using first-principles calculations. Because of the short O-O distances in the rutile structure containing cations of small effective ionic radii such as Ge4+, the antibonding interaction between O 2p orbitals raises the valence band maximum energy level to an extent that hole doping appears feasible. Experimentally, we report the flux growth of 1.5 x 1.0 x 0.8 mm(3) large rutile GeO2 single crystals and confirm the thermal stability for temperatures up to 1021 +/- 10 degrees C. X-ray fluorescence spectroscopy shows the inclusion of unintentional Mo impurities from the Li2O-MoO3 flux, as well as the solubility of Ga in the r-GeO2 lattice as a prospective acceptor dopant. The resistance of the Ga- and Mo-codoped r-GeO2 single crystals is very high at room temperature, but it decreases by 2-3 orders of magnitude upon heating to 300 degrees C, which is attributed to thermally activated p-type conduction.

DOI： 10.1021/acs.jpcc.0c07757

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acsami.0c05181

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

In this work, (BaxSr1-x)Si-2 thin films were prepared by the co-sputtering method at various deposition temperatures. The constituent phase of the films primarily depended on the deposition temperature and the composition x. The composition to make a solid solution was expanded by lowering the deposition temperature, compared to that of bulk-sintered bodies. Further lowering the deposition temperature produced a metastable phase, which was a layered structure (trigonal, EuGe2-type structure), with a low thermoelectric power factor. Substitution with Ba led to an increase in the temperature showing the highest power factor. The samples with Ba concentrations over 17% showed the maximum power factor around room temperature. (c) 2020 The Japan Society of Applied Physics

DOI： 10.7567/1347-4065/ab645b

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掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society (APS)  

DOI： 10.1103/physrevb.101.125206

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その他リンク： https://link.aps.org/article/10.1103/PhysRevB.101.125206

記述言語：日本語   出版者・発行元：公益社団法人 応用物理学会  

DOI： 10.11470/jsapmeeting.2020.1.0_3583

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1557/adv.2020.67

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Amorphous oxide semiconductors (AOSs) represented by amorphous In-Ga-Zn-O have been applied for state-of-the-art flat panel displays as thin-film transistor backplane since 2012. Understanding defects in AOS is critically important for controlling the instability of TFTs. It is found in the past decades that many AOS defects arc related to oxygen and hydrogen impurities, though oxygen is the major constituent of AOS and hydrogen is not intentionally incorporated.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper presents an optical sensor based onamorphous In-Ga-Zn-O(a-IGZO) photo thin-film transistors (TFTs). To maintain a high signal-to-noise ratio (SNR) of the optical sensor against a variety of ambient white light, this paper employed a-IGZO photo-TFTs for detecting optical input signal sensitive only to short-wavelength light. Measurements of the photosensitivity for optical signal with different wavelengths and optical response for optical input signal under various white light irradiances are proposed to support the reliability of the a-IGZO photo-TFTs under different ambient white light conditions. This paper also simulates a-IGZO photo-TFTs under various white light conditions to predict and design the proposed new sensors and circuits. The simulation results indicated that the proposed optical sensor can maintain the obvious difference in the output voltages with or without optical input signal under the white light irradiances of 0, 268, and 750 mu W/cm(2), demonstrating the feasibility and the reliability of the proposed optical pixel sensor.

DOI： 10.1109/TED.2019.2925091

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

SrTiN2 is expected to exhibit unique carrier transport properties since it has a two-dimensional (2D) electron transport layer in its natural layered crystal structure, and its conduction band minimum is formed mainly of Ti 3d(xy) orbitals similar to the SrTiO3-based 2D electron gas system. However, only-nearly metallic conduction has been reported for SrTiN2, which is probably due to difficulty in synthesizing high purity, low defect density samples. In this paper, we report a density functional theory study to determine the origin of the unintentional high carrier generation and to design the synthesis routes to high purity SrTiN2 with high controllability of carrier doping. We found that SrTiN2 is thermodynamically stable in a wide chemical potential window from N-poor to N-rich conditions, but high-density residual electrons are generated at the N-poor condition due to the easy formation of N vacancies (V-N). The formation of V-N is suppressed at larger N chemical potentials, but unintentional incorporation of O impurity at N sites in turn produces a donor even in the high N chemical potential conditions, indicating the synthesis condition should be tuned in the N-moderate conditions in equilibrium with SrN to obtain high purity SiTiN2 with low defect densities. For hydrogen impurities, all p-type H-related defects are compensated by other n-type H-related defects in the N-moderate conditions, and thus H impurity produces no efficient carriers. As for extrinsic dopants, La works as a shallow donor for any N chemical potentials while Y and Nb work only at the N-poor and N-rich conditions. Meanwhile, SrTiN2 is hard to convert to p-type because the acceptor candidates, e.g., Na, K, Rb at Sr site, have high formation energy and are compensated by V-N and O-N donors.

DOI： 10.1021/acs.jpcc.9b03643

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Multi-color inorganic thin-film phosphors are deposited at room temperature on glass substrates using ultra-wide bandgap amorphous gallium oxide (a-GO) as a host material. All of the a-GO films doped with four kinds of rare-earth ions (a-GO:REx) emit visible light, originating from the RE ions, by 238-257 nm ultraviolet light excitation; that is, blue & red emission from RE = Pr3+, red from Sm3+, green from Tb3+, and blue and yellow from Dy3+. The a-GO:Pr-x and a-GO:Tb-x films emit bright light clearly visible by human eyes. Although the internal quantum efficiencies of unannealed a-GO:Pr-0.02 and a-GO:Tb-0.02 films are 0.2 and 1.8%, respectively, those are improved to 2.4 and 3.8 %, respectively, by post-deposition thermal annealing in O-2 at 400 degrees C through desorption of weakly-bonded oxygen and structural relaxation. On the other hand, the annealing temperature to improve photoluminescence is limited by crystallization (onset temperatures 400-500 degrees C).

DOI： 10.1002/pssa.201700833

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Amorphous oxide semiconductors (AOSs) have been commercialized since 2012 as thin-film transistor (TFT) backplanes in flat-panel displays. This review first provides a brief history and current status of AOS technology, and then introduces electronic defects in AOSs reported to date that are critically important for understanding and controlling the instability of TFTs that is the most serious issue in the development of the AOS technology. In particular, it is important to know that many AOS defects are related to oxygen and hydrogen impurities, though oxygen is the major constituent of AOS and hydrogen is not intentionally incorporated. Instability issues and their underlying mechanisms are also discussed in relation to these defects.

DOI： 10.1002/pssa.201800372

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

It is generally thought that deposition of device-quality oxide semiconductors requires somewhat high oxygen supply in order to reduce oxygen deficiency and to suppress generation of free electrons. This paper reports that such high oxygen supply is not an essential requirement for a representative amorphous oxide semiconductor, amorphous In-Ga-Zn-O (a-IGZO). That is, the optimum oxygen flow rate ratio (R-O2) is approximate to 3% for standard (STD) sputtering with the base pressure of approximate to 10(-4) Pa, while it is reduced dramatically to 10(-3)-10(-5)% for ultrahigh vacuum (UHV) sputtering with the base pressure of approximate to 10(-7) Pa. We consider that the ultralow optimum oxygen supply originates from residual hydrogen, because the STD and the UHV films have different hydrogen contents at the orders of 10(20) and 10(19) cm(-3), respectively. This comparison also suggests that the inclusion of impurity hydrogen widens the optical bandgap by approximate to 0.1 eV, which causes a bandgap minimum by post annealing at approximate to 500 degrees C for the STD a-IGZO films accompanying the removal of incorporated hydrogen as H2O. Furthermore, crystallization onset temperature is reduced remarkably by approximate to 100 K for the UHV a-IGZO films.

DOI： 10.1002/pssa.201700832

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.99.035148

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Physics Publishing  

DOI： 10.7567/1347-4065/ab148c

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.5117771

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ROYAL SOC CHEMISTRY  

Hydrogen (H) plays critical roles in the electrical properties of semiconductor materials and devices. In this work, we report multiple states and roles of H in SnS by H plasma treatment and density functional theory (DFT) calculations. The as-deposited SnS films include impurity H at 2.3 x 10(19) cm(-3), four orders of magnitude larger than the hole density. The DFT calculations reveal that H exists in multiple states at the equilibrium mainly at the interstitial and the Sn-substitutional sites, which have formation enthalpies lower than those for the intrinsic defects. These H states work as donors and acceptors, respectively, and strongly pin the Fermi level in the p-type region. The native p-type conduction in the actual SnS semiconductors is caused mainly by the H-on-Sn (H-Sn) acceptors, rather than the previously reported Sn vacancies (V-Sn) for pure SnS. It is also confirmed that even stronger H doping with larger H chemical potentials cannot convert SnS to an n-type conductor because it reduces SnS to Sn metal.

DOI： 10.1039/c8cp02261e

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.inorgchem.7b01510

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

The electronic structures of the antifluorite-type compound Mg2Si is described in which a sublattice of short cation-cation contacts creates a very low conduction band minimum. Since Mg2Si shows n-type conductivity without intentional carrier doping, the present result indicates that the cage defined by the cations plays critical roles in carrier transport similar to those of inorganic electrides, such as 12CaO center dot 7Al(2)O(3):e(-) and Ca2N. A distinct difference in the location of conduction band minimum between Mg2Si and the isostructural phase Na2S is explained in terms of factors such as the differing interaction strengths of the Si/S 3s orbitals with the cation levels, with the more core-like character of the S 3s leading to a relatively low conduction band energy at the G point. Based on these results and previous research on electrides, approaches can be devised to control the energy levels of cation sublattices in semiconductors.

DOI： 10.1002/anie.201701681

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Insulator-like FeSe epitaxial thin films were grown at three different growth conditions (i.e., at Fe flux rates = 2, 4, and 6 x 10(-6) Pa under a constant Se flux rate), and the superconducting properties induced by electric double-layer transistors (EDLTs) were investigated in relation to the crystal/defect structures of the FeSe channels. The maximum critical temperature (T-c) of 35 K was obtained for the FeSe channel grown at the intermediate Fe flux rate. The other EDLTs (i.e., grown at a higher and a lower Fe flux rates, respectively) exhibited lower Tc of approximate to 20 K, which were in the under-and the overdoped states, respectively, as confirmed by Hall effect measurements. The underdoped state of the channel grown at the higher rate is explained by electron traps at surface pits. This study revealed that high crystallinity and atomically flat surfaces are the key factors to achieving the optimum doping level and inducing the high Tc in insulator-like FeSe EDLTs.

DOI： 10.1109/TASC.2016.2639738

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Wiley-Blackwell  

DOI： 10.1002/sdtp.12047

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We optimized the substrate temperature (T-s) and phosphorus concentration (x) of BaFe2(As1-xPx)(2) films on practical metal-tape substrates for pulsed laser deposition from the viewpoints of crystallinity, superconductor critical temperature (T-c), and critical current density (J(c)). It was found that the optimum T-s and x values are 1050 degrees C and x = 0.28, respectively. The optimized film exhibits T-c(onset) = 26.6 and T-c(zero) = 22.4 K along with a high self-field J(c) at 4 K (similar to 1 MAcm(-2)) and relatively isotropic J(c) under magnetic fields up to 9 T. Unexpectedly, we found that lower crystallinity samples, which were grown at a higher T-s of 1250 degrees C than the optimized T-s = 1050 degrees C, exhibit higher J(c) along the ab plane under high magnetic fields than the optimized samples. The presence of horizontal defects that act as strong vortex pinning centers, such as stacking faults, are a possible origin of the high J(c) values in the poor crystallinity samples.

DOI： 10.1088/1361-6668/aa621c

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

The high room temperature mobility and the electron effective mass in BaSnO3 are investigated in depth by evaluation of the free carrier absorption observed in infrared spectra for epitaxial films with free electron concentrations from 8.3x10(18) to 7.6x10(20) cm(-3). Both the optical band gap widening by conduction band filling and the carrier scattering mechanisms in the low- and high-doping regimes are consistently described employing parameters solely based on the intrinsic physical properties of BaSnO3. The results explain the current mobility limits in epitaxial films and demonstrate the potential of BaSnO3 to outperform established wide-band gap semiconductors also in the moderate doping regime.

DOI： 10.1103/PhysRevB.95.161202

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

The variety of semiconductor materials has been extended in various directions, for example, to very wide bandgap materials such as oxide semiconductors as well as to amorphous semiconductors. Crystalline beta- Ga2O3 is known as a transparent conducting oxide with an ultra- wide bandgap of similar to 4.9 eV, but amorphous (a-) Ga2Ox is just an electrical insulator because the combination of an ultra-wide bandgap and an amorphous structure has serious difficulties in attaining electronic conduction. This paper reports semiconducting a-(GaOx)-O-2 thin films deposited on glass at room temperature and their applications to thin-film transistors and Schottky diodes, accomplished by suppressing the formation of charge compensation defects. The film density is the most important parameter, and the film density is increased by enhancing the film growth rate by an order of magnitude. Additionally, as opposed to the cases of conventional oxide semiconductors, an appropriately high oxygen partial pressure must be chosen for a-Ga2Ox to reduce electron traps. These considerations produce semiconducting a-Ga2Ox thin films with an electron Hall mobility of similar to 8 cm(2)V(-1) s (-1), a carrier density Ne of similar to 2x10(14) cm-3 and an ultra-wide bandgap of similar to 4.12 eV. An a-Ga2Ox thin-film transistor exhibited reasonable performance such as a saturation mobility of similar to 1.5 cm(2) V-1 s -1 and an on/ off ratio 4107.

DOI： 10.1038/am.2017.20

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Microstructures of amorphous In-Ga-Zn-O (a-IGZO) thin films of different densities were analyzed. Device-quality a-IGZO films were deposited under optimum conditions, e.g., the total pressure P-tot = 0.55 Pa produced high film densities of similar to 6.1 g/cm(3), while a very high P-tot = 5.0 Pa produced low film densities of 5.5 g/cm(3). Both films formed uniform high-density layers in the vicinity of the glass substrate, 10-20nm in thickness depending on Ptot, while their growth mode changed to a sparse columnar structure in thicker regions. X-ray reflectivity and in situ spectroscopic ellipsometry provided different results on densification by post deposition thermal annealing; i.e., the latter has a higher sensitivity. High-Z-contrast images obtained by high-angle annular dark-field scanning transmission electron microscopy were also useful for detecting nanometer-size non uniformity even in device-quality a-IGZO films. (C) 2017 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.56.03BB03

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

Efficient electron transfer between a cathode and an active organic layer is one key to realizing high-performance organic devices, which require electron injection/transport materials with very low work functions. We developed two wide-bandgap amorphous (a-) oxide semiconductors, a-calcium aluminate electride (a-C12A7:e) and a-zinc silicate (a-ZSO). A-ZSO exhibits a low work function of 3.5 eV and high electron mobility of 1 cm(2)/(V . s); furthermore, it also forms an ohmic contact with not only conventional cathode materials but also anode materials. A-C12A7:e has an exceptionally low work function of 3.0 eV and is used to enhance the electron injection property from a-ZSO to an emission layer. The inverted electron-only and organic light-emitting diode (OLED) devices fabricated with these two materials exhibit excellent performance compared with the normal type with LiF/Al. This approach provides a solution to the problem of fabricating oxide thin-film transistor-driven OLEDs with both large size and high stability.

DOI： 10.1073/pnas.1617186114

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELECTROCHEMICAL SOC INC  

We report new amorphous oxide semiconductor (AOS)-based thin film phosphor, Eu-doped a-Ga2Ox (a-GO:Eu), to solve the issues of previously reported a-In-Ga-Zn-O: Eu (a-IGZO:Eu). The internal quantum efficiencies (IQE) of a-GO:Eu (2.3% for unannealed, 8.3% for annealed films) are improved from those of a-IGZO:Eu (0.9% and 1.6%, respectively) because of the much wider bandgap (4.26 eV), subsequent low residual electron density, and higher available annealing temperature. We found that the annealing temperature to improve IQE is limited by crystallization temperature. Another issue of a-IGZO:Eu is that the initial state of Eu3+ 4f is deeper than the valence band maximum (VBM), which is not suitable for light-emitting diode. We expected that Eu3+ 4f would locate above the VBM in a-GO:Eu because the VBM of a-Ga2Ox is similar to 0.8 eV deeper than that of a-IGZO. However, resonant photoemission spectroscopy revealed that the Eu 4f states are bound more to the O 2p valence band than to the vacuum level, and the Eu3+ 4f states in a-GO:Eu are still buried in the valence band. (C) 2017 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0181707jss

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELECTROCHEMICAL SOC INC  

The roles of hydrogen introduced by post-deposition hydrogen treatments were investigated for amorphous In-Ga-Zn-O (a-IGZO) films using room-temperature hydrogen plasma (H-plasma) and high-temperature H-2 annealing. It was found that these treatments cause different effects as confirmed by hard X-ray photoemission spectroscopy and difference spectrum analyses. The H-plasma treatment increased both the near-valence band maximum (near-VBM) states (observed just above VBM) and the -OH bonds (confirmed by O 1s core spectrum) if a-IGZO films were deposited under an optimum condition, leading to the conclusion that the room-temperature H treatment incorporates H to a-IGZO films as -OH bonds, and the increase in the relatively shallow near-VBM states (peaked at similar to 1.0 eV, extended to similar to 2.4 eV from VBM) is ascribed to the generated -OH bonds. On the other hand, high-temperature H-2 annealing did not increase the O 1s -OH signal, and its difference spectrum showed a different peak centered at similar to 0.7 eV. This difference spectrum is similar to that of H-less a-IGZO films deposited without O-2 supply by ultra-high vacuum sputtering and assigned to oxygen deficiency. These results will contribute to control the operation characteristics and the instability issues of a-IGZO TFTs. Further, the deconvoluted difference spectra will be the standard fingerprints of these defects in a-IGZO. (C) 2017 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0071707jss

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記述言語：英語   出版者・発行元：ELECTROCHEMICAL SOC INC  

DOI： 10.1149/2.0171708jss

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記述言語：英語   出版者・発行元：ELECTROCHEMICAL SOC INC  

DOI： 10.1149/2.0171708jss

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We selected BaZn2As2 as a candidate for a high-mobility p-type amorphous semiconductor because of the valence band maximum formed mainly of widely spread As 4p orbitals. The hole mobility of amorphous BaZn2As2 films increased from 1 to 10 cm(2) V-1 s(-1) as the annealing temperature increased from 300 to 400 degrees C. 500 degrees C annealing started crystallizing the film with the hole mobility similar to 20 cm(2) V-1 s(-1). The optical bandgaps of amorphous BaZn2As2 were 1.04-1.37 eV, which are much larger than that of the crystalline beta-BaZn2As2 (0.23 eV). It is explained by the broken symmetry at the Ba site and the weakening of the As-As direct bonds, which is supported by 6 keV hard X-ray photoemission spectroscopy measurement. Published by AIP Publishing.

DOI： 10.1063/1.4972039

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Thin films of the iron-based superconductor BaFe2(As1-xPx)(2) (Ba122:P) were fabricated on polycrystalline metal-tape substrates with two kinds of in-plane grain boundary alignments (well aligned (4 degrees) and poorly aligned (8 degrees)) by pulsed laser deposition. The poorly aligned substrate is not applicable to cuprate-coated conductors because the in-plane alignment &gt; 4 degrees results in exponential decay of the critical current density (J(c)). The Ba122:P film exhibited higher J(c) at 4 K when grown on the poorly aligned substrate than on the well-aligned substrate even though the crystallinity was poorer. It was revealed that the misorientation angles of the poorly aligned samples were less than 6 degrees, which are less than the critical angle of an iron-based superconductor, cobalt-doped BaFe2As2 (similar to 9 degrees), and the observed strong pinning in the Ba122:P is attributed to the high-density grain boundaries with the misorientation angles smaller than the critical angle. This result reveals a distinct advantage over cuprate-coated conductors because well-aligned metal-tape substrates are not necessary for practical applications of the iron-based superconductors.

DOI： 10.1038/srep36828

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier B.V.  

DOI： 10.1016/j.tsf.2016.07.054

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

We investigated the effects of thermal annealing for high-density subgap states in amorphous In-Ga-Zn-O (a-IGZO) films by focusing on low-quality defective films deposited without O-2 supply (LQ films). It was found that most of the subgap states were thermally unstable and decreased dramatically by annealing at &lt;= 400 degrees C in O-2. These defects (but with different shapes) were further reduced by 600 degrees C annealing, whose subgap states appeared similar to that of a-IGZO films deposited at an optimum condition (high quality, HQ films) and annealed at 300 degrees C. However, electron Hall mobilities and field-effect mobilities of their thin-film transistors (TFTs) were low for the LQ films/TFTs even annealed at 600 degrees C compared to those for the HQ films/TFTs. It implies that not only the subgap states but also heavier structural disorder deteriorated the electron transport in the LQ films. The present results also suggest that although a-IGZO deposition without O-2 supply is sometimes employed in particular for DC sputtering, supplying some O-2 gas would be better to produce good TFTs at lower temperatures. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2016.03.005

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

We fabricated amorphous oxide semiconductor films, a-(Ga1-xZnx)O-y, at room temperature on glass, which have widely tunable band gaps (E-g) ranging from 3.47-4.12 eV. The highest electron Hall mobility similar to 7 cm(2) V-1 s(-1) was obtained for E-g = similar to 3.8 eV. Ultraviolet photoemission spectroscopy revealed that the increase in E-g with increasing the Ga content comes mostly from the deepening of the valence band maximum level while the conduction band minimum level remains almost unchanged. These characteristics are explained by their electronic structures. As these films can be fabricated at room temperature on plastic, this achievement extends the applications of flexible electronics to opto-electronic integrated circuits associated with deep ultraviolet region. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2016.03.003

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Wiley-Blackwell  

DOI： 10.1002/sdtp.10883

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

We succeeded in fabricating light-emitting amorphous oxide (LEAO) thin films by doping Eu3+ ions to amorphous In-Mg-O deposited at room temperature using (In, Eu)(2)MgO4 polycrystalline targets by pulsed laser deposition. Clearly visible photoluminescence (PL) with a peak at 615 nm was observed at room temperature by 270 nm light excitation even without post-deposition thermal annealing. The unusual variation of PL intensity with Eu concentration is understood in terms of non-radiative Auger recombination via conduction carriers. The PL intensity also exhibited maximums with respect to oxygen pressure during deposition (PO2) and annealing temperature (T-a), which are explained by recombination centers generated by oxygen deficiency-related defects at low PO2, by excess/weakly-bonded oxygen at high PO2, and by hydrogen depletion at high T-a. Since the LEAO films can be obtained even by room-temperature deposition, it is expected to have flexible optoelectronic applications using plastic substrates. (C) 2016 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.15283

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We propose a novel solid-phase epitaxy technique applicable to high annealing temperatures up to 1000 degrees C without re-vaporization of alkali metal elements with high vapor pressures. This technique is demonstrated through the successful growth of high-quality KFe2As2 epitaxial films. The key factors are employing a custom-designed alumina vessel/cover and sealing it in a stainless tube with a large amount of atmospheric KFe2As2 powder in tightly closed sample spaces. This technique can also be effective for other materials composed of elements with very high vapor pressures, such as alkali metals, and can lead to the realization of spintronics devices in the future using KFe2As2. (C) 2016 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.9.055505

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

DOI： 10.7567/APEX.9.051201

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATL ACAD SCIENCES  

It is thought that strong electron correlation in an insulating parent phase would enhance a critical temperature (T-c) of superconductivity in a doped phase via enhancement of the binding energy of a Cooper pair as known in high-T-c cuprates. To induce a superconductor transition in an insulating phase, injection of a high density of carriers is needed (e.g., by impurity doping). An electric double-layer transistor (EDLT) with an ionic liquid gate insulator enables such a field-induced transition to be investigated and is expected to result in a high T-c because it is free from deterioration in structure and carrier transport that are in general caused by conventional carrier doping (e.g., chemical substitution). Here, for insulating epitaxial thin films (similar to 10 nm thick) of FeSe, we report a high T-c of 35 K, which is 4x higher than that of bulk FeSe, using an EDLT under application of a gate bias of + 5.5 V. Hall effect measurements under the gate bias suggest that highly accumulated electron carrier in the channel, whose area density is estimated to be 1.4 x 10(15) cm(-2) (the average volume density of 1.7 x 10(21) cm(-3)), is the origin of the high-T-c superconductivity. This result demonstrates that EDLTs are useful tools to explore the ultimate T-c for insulating parent materials.

DOI： 10.1073/pnas.1520810113

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

This work presents the solid phase epitaxial growth of high mobility La: BaSnO3 thin films on SrTiO3 single crystal substrates by crystallization through thermal annealing of nanocrystalline thin films prepared by pulsed laser deposition at room temperature. The La: BaSnO3 thin films show high epitaxial quality and Hall mobilities up to 26 +/- 1 cm(2)/Vs. Secondary ion mass spectroscopy is used to determine the La concentration profile in the La: BaSnO3 thin films, and a 9%-16% La doping activation efficiency is obtained. An investigation of H doping to BaSnO3 thin films is presented employing H plasma treatment at room temperature. Carrier concentrations in previously insulating BaSnO3 thin films were increased to 3 +/- 10(19) cm(-3) and in La: BaSnO3 thin films from 6 x 10(19) cm(-3) to 1.5 x 10(20) cm(-3), supporting a theoretical prediction that interstitial H serves as an excellent n-type dopant. An analysis of the free electron absorption by infrared spectroscopy yields a small (H, La): BaSnO3 electron effective mass of 0.27 +/- 0.05 m(0) and an optical mobility of 26 +/- 7cm(2)/Vs. As compared to La: BaSnO3 single crystals, the smaller electron mobility in epitaxial thin films grown on SrTiO3 substrates is ascribed to threading dislocations as observed in high resolution transmission electron micrographs. Published by AIP Publishing.

DOI： 10.1063/1.4948355

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

We synthesized nonequilibrium cubic rock-salt (RS)-type (Sn,Pb)Se and investigated their optoelectronic properties with the expectation that the RS-type structure would exhibit better carrier transport properties than the equilibrium GeS-type layered crystal structure in SnSe because the RS-type structure has the three-dimensional network of (PbSe6) octahedra, while the GeS-type structure has the two-dimensional network of (SnSe3), leading to larger band dispersions and smaller carrier effective masses. To stabilize the nonequilibrium phase, epitaxial thin films were grown by a unique method, a reactive solid-phase epitaxy with a thin RS-type PbSe epitaxial template layer. Additionally, a rapid quenching process from 600 degrees C to room temperature was also effective for stabilizing the nonequilibrium RS-type (Sn,Pb)Se epitaxial films. We succeeded in controlling Pb concentration continuously from 0 to 100% in the (Sn,Pb)Se solid-solution films. The minimum Pb concentration to stabilize the RS-type SnSe was extended from the previously reported value of 63% to 50%. A band gap bowing effect was observed with the smallest estimated band gap of similar to 0.14 eV for the RS-type (Sn0.35Pb0.65)Se. The GeS-type to RS-type structural change increased hole mobility drastically from 60 for SnSe to 290 cm(2)/(Vs) for 58% Pb-doped RS-type (Sn,Pb)Se film as expected. It was found that p-type to n-type conversion occurs by further higher Pb concentrations &gt;= 61%, and the highest electron mobility of 340 cm(2)/(Vs) was observed.

DOI： 10.1021/acs.chemmater.6b00307

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記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：Springer International Publishing  

Research on oxide semiconductor has advanced significantly in the last decade. In particular, transparent amorphous oxide semiconductor (TAOS) was proposed as a novel class of amorphous semiconductors having large electron mobility comparable to those in the corresponding crystals. Since the application of TAOS to an active layer in thin-film transistors (TFTs) was reported in late 2004, extensive research on application of TAOS TFT, in particular In-Ga-Zn-O (IGZO)-based TAOS, to the backplanes of state-of-the-art flat-panel displays has been performed, and many displays driven by oxide backplanes have been commercialized. This chapter first gives a review on the history and present status of oxide semiconductors, then explains the unique nature of TAOS and advantages of TAOS over other semiconductors, and finally describes the fabrication process and condition suitable for TAOS TFTs.

DOI： 10.1007/978-3-319-14346-0_52

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We propose a light-emitting thin film using an amorphous oxide semiconductor (AOS) because AOS has low defect density even fabricated at room temperature. Eu-doped amorphous In-Ga-Zn-O thin films fabricated at room temperature emitted intense red emission at 614 nm. It is achieved by precise control of oxygen pressure so as to suppress oxygen-deficiency/excess-related defects and free carriers. An electronic structure model is proposed, suggesting that non-radiative process is enhanced mainly by defects near the excited states. AOS would be a promising host for a thin film phosphor applicable to flexible displays as well as to light-emitting transistors. (C) 2016 Author(s).

DOI： 10.1063/1.4939939

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Polycrystalline SnS thin films were fabricated by a H2S-free process combing pulsed laser deposition at room temperature and post-deposition thermal annealing in Ar. Thermal annealing improved the crystalline quality of the SnS films and the best films were obtained by 400 degrees C annealing. The obtained SnS films exhibited p-type conduction with the highest Hall mobility of 28 cm(2)/(V.s) and the carrier densities of 1.5 x 10(15) - 1.8 x 10(16) cm(-3). The SnS TFT exhibited p-type operation with a field effect mobility and an on-off drain current ratio of 0.4 cm(2)/(V.s) and 20, respectively. (C) 2016 Author(s).

DOI： 10.1063/1.4940931

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

Film density of amorphous In-Ga-Zn-O (a-IGZO) was varied in a wide range to investigate the origin of the low film density and its effect on thin-film transistor (TFT) characteristics. Device-quality a-IGZO films have the densities similar to 6.1 g/cm(3), which is similar to 5% smaller than that of single-crystal InGaZnO4 (c-IGZO) (6.4 g/cm(3)). On the other hand, extremely low density of 5.5 g/cm(3) was obtained when the sputtering working pressure (P-Tot) was increased to 5 Pa. High density desorption of H2O and O-2 was detected in the low-density films, which are attributed to an origin of the low density. Although the low-density channel produced poor TFTs, good TFT characteristics were obtained by annealing at T-ann = 300 degrees C. The densities of the low-density films obtained by X-ray reflectivity (XRR) analysis were, however, almost unchanged up to T-ann = 500 degrees C, while spectroscopic ellipsometry (SE) analysis showed that densification started from 100 degrees C. This contradiction is explained by transmission electron microscopy (TEM). Although conventional high-resolution TEM (HR-TEM) observation could not detect a microstructure in the high-density a-IGZO films, high-angle annular dark field scanning TEM (HAADF-STEM) detected nano-scale low-density regions. The low-density films had larger and more voids. These void structures were not found in very thin regions (5-10 nm from the substrate surface) but increased in thicker regions.

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DOI： 10.1063/1.4947456

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その他リンク： http://orcid.org/0000-0003-3093-3779

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

Electrides are characteristic of anionic electrons trapped at the structural voids in the host lattice. Electrides are potentially useful in various technological applications; however, electrides, particularly their inorganic subgroup, have been discovered only in limited material systems, notably zero-dimensional [Ca24Al28O64](4+):4e(-) and two-dimensional [Ca2N](+):e(-) and [Y2C](1.8+):1.8e(-). Here, on the basis of density functional theory calculations, we report the first one- dimensional (1D) electride with a [La8Sr2(SiO4)(6)](4+):4e(-) configuration, in which the four anionic electrons are confined in the channel spaces of the host material. According to this theoretical prediction, an insulator semiconductor transition originating from electron confinement in the crystallographic channel sites was demonstrated experimentally, where 10.5% of the channel oxygen was removed by reacting an oxygen stoichiometric La8Sr2(SiO4)(6)O-2 precursor with Ti metal at a high temperature. This study not only adds an unprecedented role to silicate apatite as a parent phase to a new 1D electride, but also, and more importantly, demonstrates an effective approach for developing new electrides with the assistance of computational design.

DOI： 10.1021/acs.jpclett.5b02283

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We investigated the effects of residual hydrogen in sputtering atmosphere on subgap states and carrier transport in amorphous In-Ga-Zn-O (a-IGZO) using two sputtering systems with different base pressures of similar to 10(-4) and 10(-7) Pa (standard (STD) and ultrahigh vacuum (UHV) sputtering, respectively), which produce a-IGZO films with impurity hydrogen contents at the orders of 10(20) and 10(19) cm(-3), respectively. Several subgap states were observed by hard X-ray photoemission spectroscopy, i.e., peak-shape near-valence band maximum (near-VBM) states, shoulder-shape near-VBM states, peak-shape near-conduction band minimum (near-CBM) states, and step-wise near-CBM states. It was confirmed that the formation of these subgap states were affected strongly by the residual hydrogen (possibly H2O). The step-wise near-CBM states were observed only in the STD films deposited without O-2 gas flow and attributed to metallic In. Such step-wise near-CBM state was not detected in the other films including the UHV films even deposited without O-2 flow, substantiating that the metallic In is segregated by the strong reduction effect of the hydrogen/H2O. Similarly, the density of the near-VBM states was very high for the STD films deposited without O-2. These films had low film density and are consistent with a model that voids in the amorphous structure form a part of the near-VBM states. On the other hand, the UHV films had high film densities and much less near-VBM states, keeping the possibility that some of the near-VBM states, in particular, of the peak-shape ones, originate from -OH and weakly bonded oxygen. These results indicate that 2% of excess O-2 flow is required for the STD sputtering to compensate the effects of the residual hydrogen/H2O. The high-density near-VBM states and the metallic In segregation deteriorated the electron mobility to 0.4 cm(2)/(V s). (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4936552

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Epitaxial growth of SnSe was studied using pulsed laser deposition on three kinds of single-crystalline substrates, MgO (100), NaCl (100), and SrF2 (100), along with silica glass. For polycrystalline SnSe grown on glass, we found that a 20% Se-rich polycrystalline target is effective for obtaining stoichiometric SnSe films. The crystal structure of all the obtained films was the same as that of bulk SnSe, and the optimum temperatures for epitaxial growth were 400-500 degrees C, where the highest temperature was limited by re-evaporation. All the epitaxial films exhibited an a-axis orientation. For in-plane epitaxial structures, a quasi cube-on-cube heteroepitaxy was observed for MgO, whereas a 45 degrees-rotated heteroepitaxy was observed for NaCl and SrF2, which can be explained by in-plane lattice matching. The anisotropic lattice mismatching and thermal expansion explain the compressive strain induced along the in-plane c-axis and the tensile strains along the in-plane b-axis and the out-of-plane a-axis. The epitaxial films on NaCl exhibited the best crystallinity, but the highest hole mobility of 60 cm(2)/(V s) was obtained on MgO. The indirect optical gap of the best films was determined to be 0.8 eV. Plausible interface models were proposed based on density functional calculations. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4936202

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CHEMICAL SOC JAPAN  

Cs2SnI6, a variant of perovskite CsSnI3, is gaining interest as a photovoltaic material. Based on a simple ionic model, it is expected that Cs2SnI6 is composed of Cs+, I-, and Sn4+ ions and that the band gap is primarily made of occupied I- 5p(6) valence band maximum (VBM) and unoccupied Sn4+ 5s conduction band minimum (CBM) similar to SnO2. In this work, we performed density functional theory (DFT) calculations and revealed that the real oxidation state of the Sn ion in Cs2SnI6 is +2 similar to CsSnI3. The +2 oxidation state of Sn originates from 2 ligand holes (L+) in the [SnI6](2-) octahedron unit, where the ligand [Id cluster has the apparent [I-6(6)-(L) under bar (+)(2)](4-) oxidation state, because the band gap is formed mainly by occupied I 5p VBM and unoccupied I 5p CBM. The +2 oxidation state of Sn and the band gap originate from the intracluster hybridization and stabilized by the strong covalency of the Sn-I bonds.

DOI： 10.1246/bcsj.20150110

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Effects of low temperature (300 degrees C) annealing on Cu2O films were investigated by analyzing the film stacking structures with photoemission spectroscopy, X-ray reflectivity spectroscopy and spectroscopic ellipsometory in relation to p-channel TFT characteristics and possible origins of trap states. The Hall mobility of optimum Cu2O films was 2.1 cm(2)/(V.s); however, the bottom-gate Cu2O TFT exhibited a much lower field effect mobility of the order of 10(-4) cm(2)/(V.s) and an on/ off drain current ratio of 10(3). This work detected a surface layer and an interface layer in the Cu2O/SiO2 samples, i.e., the surface layer included the state of Cu ions that would form subgap hole trap states at the back channel region. In addition, the low-density layer at the Cu2O-SiO2 interface would produce extra interfacial trap states.

DOI： 10.1109/JDT.2015.2432752

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：A V S AMER INST PHYSICS  

Polycrystalline Cu2O films were fabricated on amorphous SiO2 glass by pulsed laser deposition at room temperature and postdeposition thermal annealing in N-2 + O-2 mixing gases. The authors made a phase map in annealing temperature (T-ann) vs R-O2 = [O-2]/([O-2] +[N-2]) ratio and found that highly pure Cu2O films were obtained at R-O2 similar to 0.002%. The increase in T-ann improved the crystal quality of the Cu2O films, and the maximum Hall mobility of similar to 26 cm(2)/(V s) was obtained at 700 degrees C. Bottom-gate Cu2O thin-film transistors (TFTs) using the optimum Cu2O channels exhibited clear p-type operation; however, the largest field effect mobility is as small as the order of 10(-2) cm(2)/(V s), indicating the existence of high-density hole trap states. Several subgap states were observed by optical absorption spectra of films and photoresponse spectroscopy of the TFTs. X-ray reflectivity analysis detected a low-density dead layer at the Cu2O-SiO2 glass substrate interface, which would be attributed to Cu diffusion into the glass substrate. (C) 2015 American Vacuum Society.

DOI： 10.1116/1.4929445

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Growth of amorphous ZnO by B doping and their opto-electrical properties are reported. The B-doped ZnO (ZnO:B) films were grown by pulsed laser deposition using polycrystalline ZnO:B ceramic targets. Although the solubility limit of B in bulk ZnO polycrystal was similar to 4%, 18%-doped ZnO:B showed the shrinkage in the c-axis length. Preferentially (002)-oriented polycrystalline ZnO:B films were grown for the B concentration [B] &lt;= 18%; while, amorphous ZnO:B films were obtained for [B] similar to 26%. It was found that the density of the amorphous ZnO:B film was smaller by 9% than that of crystalline ZnO (5.61 g.cm(-3)), which is explained mainly by the incorporation of the light B atoms. The optical bandgap of the ZnO:B films increased with [B] and that of the amorphous ZnO:B film was similar to 3.38 eV. The amorphous ZnO:B films have low free electron density of similar to 10(15) cm(-3), suggesting the existence of electron traps. Hall mobility of the amorphous ZnO:B [similar to 1 cm(2)(V.s)(-1)] was smaller than those of the polycrystalline ZnO:B films. (C) 2015 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.123.523

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

Amorphous InGaZnO4-xSx thin films were fabricated using a polycrystalline InGaZnO4 target by pulsed laser deposition in an H2S gas flow. The optical band gap first decreased from 3.05 to 1.65 eV as x increased from 0 to 1.5, and then increased to 2.6 eV at larger x, showing a bandgap bowing behavior. All the sulfur-containing films have high resistance beyond our measurement limit. Film density of the a-InGaZnS4 film was decreased by similar to 40% from that of a-InGaZnO4. Density functional theory calculations were performed to explain these results. (C) 2015 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.123.537

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) are employed in current flat-panel displays. It is known that deposition conditions and post-deposition thermal annealing affect structure and electrical properties of a-IGZO thin films. It was previously reported that total pressure during sputter-deposition deteriorates subthreshold swing, defect density and operation characteristics of a-IGZO TFTs. Here, we provide comprehensive results on effects of total pressure on film density, chemical composition, and TFT characteristics. Rutherford backscattering measurements detected a small amount of argon incorporated in all of the a-IGZO films. We found that increasing the total pressure deteriorated TFT characteristics; i.e., saturation mobility was dropped from 10 to 4 cm(2)/(V.s), subthreshold swing was increased from 0.2 to 0.5 V/dec, and threshold voltage was positive-shifted from 2 to 15 V. It is related to increased oxygen concentration and decreased weight density of the a-IGZO films. Thermal desorption spectra showed that amounts of weakly-bonded oxygen increased as the total pressure increased, which is considered to be related to the TFT deterioration.

DOI： 10.1109/JDT.2014.2359746

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Phosphorus-doped BaFe2As2 (BaFe2As2 : P) epitaxial films were fabricated on (La, Sr)(Al, Ta)O-3 single-crystal substrates, and their crystallinity, microstructure, and transport critical current density (J(c)) properties were characterized. Compared with those of previously reported BaFe2As2 : P epitaxial films on MgO substrates, a decrease in the self-field J(c) and strong pinning properties along the c-axis under high magnetic fields were observed. These results can be understood by considering the poor crystallinity and the large density of the domain boundary pinning centers of the present films on (La, Sr)(Al, Ta)O-3, which would be caused by a thin reaction layer produced between the BaFe2As2 : P film and the (La, Sr)(Al, Ta)O-3 substrate.

DOI： 10.1109/TASC.2014.2368073

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Tin monosulfide (SnS) is a naturally p-type semiconductor with a layered crystal structure, but no reliable n-type SnS has been obtained by conventional aliovalent ion substitution. In this work, carrier polarity conversion to n-type was achieved by isovalent ion substitution for polycrystalline SnS thin films on glass substrates. Substituting Pb2+ for Sn2+ converted the majority carrier from hole to electron, and the free electron density ranged from 10(12) to 10(15) cm(-3) with the largest electron mobility of 7.0 cm(2)/(Vs). The n-type conduction was confirmed further by the position of the Fermi level (EF) based on photoemission spectroscopy and electrical characteristics of pn heterojunctions. Density functional theory calculations reveal that the Pb substitution invokes a geometrical size effect that enlarges the interlayer distance and subsequently reduces the formation energies of Sn and Pb interstitials, which results in the electron doping.

DOI： 10.1038/srep10428

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

SnS is intrinsically a p-type semiconductor, and much effort has been made to attain n-type conduction. In this letter, we performed density functional theory calculations to seek an effective doping route for n-type SnS. It was found that aliovalent doping of SnS by Sb or Bi is not effective due to their high formation enthalpies; while the isovalent Pb-substitution of the Sn sites largely reduces formation enthalpies of Sn and Pb interstitials, which explain the recently demonstrated n-type conduction in the Sn1-xPbxS films fabricated under low H2S pressures. (c) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4918294

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4913691

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ROYAL SOC CHEMISTRY  

Cs2SnI6, a rarely studied perovskite variant material, is recently gaining a lot of interest in the field of photovoltaics owing to its nontoxicity, air-stability and promising photovoltaic properties. In this work, we report intrinsic defects in Cs2SnI6 using first-principles density functional theory calculations. It is revealed that iodine vacancy and tin interstitial are the dominant defects that are responsible for the intrinsic n-type conduction in Cs2SnI6. Tin vacancy has a very high formation energy (&gt;3.6 eV) due to the strong covalency in the Sn-I bonds and is hardly generated for p-type doping. All the dominant defects in Cs2SnI6 have deep transition levels in the band gap. It is suggested that the formation of deep defects can be suppressed significantly by employing an I-rich synthesis condition, which is inevitable for photovoltaic and other semiconductor applications.

DOI： 10.1039/c5cp03102h

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Electrochemical Society Inc.  

Electronic devices using oxide semiconductor based thin-film transistors (TFTs) were commercialized for the first time in 2012 as backplane active-matrix circuits for flat-panel displays after almost half a century from their first demonstration in 1964. Such a miraculous revival was induced by discovery of high-mobility semiconductor materials made from amorphous oxides of post-transition metals and invention of TFTs using them for their channel materials in 2004. The present paper provides a historical review of oxide semiconductor based TFTs, their recent advances in the recent decade along the strategy and scenario, and a prediction of their future.

DOI： 10.1149/06701.0003ecst

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELECTROCHEMICAL SOC INC  

Effects of Pb doping on the microstructural, optical, and hole transport properties of Sn1-xfPbxfO films fabricated by pulsed laser deposition were investigated. It was found that Pb was not solved in bulk ceramic samples, while solved up to x(f) = 0.035 in the thin films. The Pb doping enlarged the optical bandgap, decreased the hole concentration, and reduced the Hall mobility (mu(Hall), from 1.95 to 0.68 cm(2) V-1 s(-1) up to x(f) = 0.035) as xf increased. The field-effect mobility in thin-film transistors also decreased with xf (mu(lin), from 0.34 to 0.0024 cm(2) V-1 s(-1)), but the deterioration of mu(lin) was significantly larger than that of mu(Hall). It is speculated that the deterioration of mu(Hall) would be due to the increase in grain boundary potential barriers. The deterioration of mu(lin), low on-state current, and high off-state current are explained semiquantitatively by a simple hole trap model. Similar explanations would be applied also to previous reports on Sb/Y doped-SnO. Location of the highest occupied states of Pb2+ relative to that of Sn2+ (i.e., Pb 6s(2) and Sn 5s(2), respectively) clarified by DFTcalculations provides an explantion for the observed result. (C) 2015 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0231503jss

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We report operation characteristics of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) annealed in dry O-2 at temperatures up to 700 degrees C. The largest TFT mobilities were obtained by annealing at 200 degrees C-300 degrees C and the smallest subthreshold voltage swing (S) was obtained at 200 degrees C, while those annealed at higher T exhibited poorer mobilities and S values. The TFTs annealed at &gt;= 600 degrees C were crystallized and exhibited further poorer characteristics probably due to grain boundary issues; while, the deterioration by the 400 degrees C-500 degrees C annealing is attributed to depletion of hydrogen and consequent de-passivation effects. Device simulations and photoresponse spectroscopy extracted systematic variation of trap densities in the a-IGZO layer.

DOI： 10.1109/JDT.2014.2352860

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

Electrides are ionic crystals in which the anionic electrons are confined to interstitial subnanometer-sized spaces. At present, the reported electrides only consist of main-group elements. Here, we report a layered-structure transition-metal hypocarbide electride, Y2C, with quasi-two-dimensional (quasi-2D) anionic electrons confined in the interlayer space. Physical properties measurements reveal polycrystalline Y2C exhibits semimetallic behavior, and paramagnetism with an effective magnetic moment of similar to 0.6 mu(B)/Y, because of the existence of localized d-electrons. Photoelectron spectroscopy measurements illustrate the work function of polycrystalline Y2C is 2.9 eV, lower than Y metal, revealing the loosely bound nature of the anionic electrons. Density functional theory calculations indicate the density of states at the Fermi level originates from the states at interstitial sites and the Y 4d-orbitals, supporting the confinement of anionic electrons within the interlayer space. These results demonstrate that Y2C is a quasi-2D electride in term of [Y2C](1.8+).1.8e , and the coexistence of the anionic electrons and the Y 4d-electrons leads to the semimetallic behavior.

DOI： 10.1021/cm503512h

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We performed constant positive gate bias stress tests on sputter-deposited amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) fabricated with various annealing conditions. We found that the time evolution of threshold voltage shift (Delta V-th) during the stress test exhibits two different behaviors; a power function type and a logarithmic function type. Combining with thermal desorption spectroscopy (TDS), we found that the Delta V-th type changes fromthe log-function type to the power-function type as H desorption increases. The power-function type is attributed to a H-diffusion limited process. As for the log-function type, the magnitude of Delta V-th has correlation with the hysteresis width in a first transfer curve and the desorption amount of H2O and O-2 species between 200 degrees C-300 degrees C. Hence, it is considered that the traps causing the log-function type Delta V-th are meta-stable states related to O- and/or OH-related weak bonds.

DOI： 10.1109/JDT.2014.2350518

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

beta-BaZn2As2 is known to be a p-type semiconductor with the layered crystal structure similar to that of LaZnAsO, leading to the expectation that beta-BaZn2As2 and LaZnAsO have similar bandgaps; however, the bandgap of beta-BaZn2As2 (previously reported value similar to 0.2 eV) is 1 order of magnitude smaller than that of LaZnAsO (1.5 eV). In this paper, the reliable bandgap value of beta-BaZn2As2 is determined to be 0.23 eV from the intrinsic region of the temperature dependence of electrical conductivity. The origins of this narrow bandgap are discussed based on the chemical bonding nature probed by 6 keV hard X-ray photoemission spectroscopy, hybrid density functional calculations, and the ligand theory. One origin is the direct AsAs hybridization between adjacent [ZnAs] layers, which leads to a secondary splitting of As 4p levels and raises the valence band maximum. The other is that the nonbonding Ba 5d(x2y2) orbitals form an unexpectedly deep conduction band minimum (CBM) in beta-BaZn2As2 although the CBM of LaZnAsO is formed mainly of Zn 4s. These two origins provide a quantitative explanation for the bandgap difference between beta-BaZn2As2 and LaZnAsO.

DOI： 10.1021/ja507890u

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER CHEMICAL SOC  

KFe2As2, an iron-based superconductor, is expected to exhibit large spin Hall conductivity, and fabrication of high-quality thin films is requisite for evaluation of this effect and application to spintronics devices. Thin-film growth of KFe2As2 is difficult because of two intrinsic properties; its extremely hygroscopic nature and the high vapor pressure of potassium. We solved these issues by combining room-temperature pulsed laser deposition using K-rich KFe2As2 targets with thermal crystallization in KFe2As2 powder after encapsulation in an evacuated silica-glass tube with all of the processes conducted in a vacuum chamber and a dry Ar atmosphere in a glovebox. The optimized KFe2As2 films on (La,Sr)(Al,Ta)O-3 single-crystal substrates were obtained by crystallization at 700 degrees C, and they were strongly c-axis oriented. The electrical measurements were performed with thin films protected by grease passivation to block reaction with the atmosphere. The KFe2As2 films exhibited a superconductivity transition at 3.7 K.

DOI： 10.1021/am5036016

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Origin of constant positive gate bias stress instability in amorphous In-Ga-Zn-O thin-film transistor is studied. Threshold voltage shift (Delta V-th) during the stress test exhibits two different behaviors: 1) a power function-type and 2) a logarithmic function-type depending on thermal treatment atmosphere and temperature. Thermal desorption spectroscopy indicated that the Delta V-th behavior changes from the log-function type to the power-function type as the amount of H-2 desorption increases. Furthermore, the recovery behavior of Delta V-th was not affected by gate bias. These results are explained by a diffusion-limited process of neutral hydrogen, which occurs within 2 nm in the vicinity of the channel-insulator interface.

DOI： 10.1109/LED.2014.2327234

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

We fabricated ZnS:(Cu, Al) thin film phosphors on glass substrates by pulsed laser deposition (PLD) using a KrF 248 nm laser in a H2S gas flow. Firstly, we investigated effects of annealing temperature, stress and crystallinity on photoluminescence properties of powder samples. For thin films, photoluminescence intensity increased with increasing the substrate temperature up to 700 degrees C and then decreased. The former increase is attributed to improvement of crystalline quality and strain, while the latter degradation is attributed to reduction of the Cu acceptors. Intense photoluminescence is observed under an ambient light when excited by 325 nm monochromated light from a fluorescence spectrophotometer. It was confirmed that the PLD process stabilized the wurtzite structure, which is not stable in bulk samples at the thermal equilibrium. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2013.11.058

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

A device model for amorphous In-Ga-Zn-O thin-film transistors (a-IGZO TFTs) that explains temperature dependence is proposed. It incorporates a carrier-density dependent mobility and a density of subgap traps of a-IGZO. The model parameters were extracted from only one transfer curve of an a-IGZO TFT at a low drain voltage through a simple analytical model. Device simulation based on this model reproduced current-and mobility-gate voltage characteristics of the a-IGZO TFT well over a wide range of bias voltage and temperature (253-393 K). (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2013.11.066

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

BaZn2As2 is expected for a good p-type semiconductor and has two crystalline phases of an orthorhombic alpha phase and a higher-symmetry tetragonal beta phase. Here, we report that high-quality epitaxial films of the tetragonal beta-BaZn2As2 were grown on single-crystal MgO (001) substrates by a reactive solid-phase epitaxy technique. Out-of-plane and in-plane epitaxial relationships between the film and the substrate were BaZn2As2 (001)//MgO (001) and BaZn2As2 [200]//MgO [200], respectively. The full-widths at halfmaximumwere 0.082 degrees for a 008 out-of- plane rocking curve and 0.342 degrees for a 200 in-plane rocking curve. A step-and-terrace structure was observed by atomic force microscopy. The band gap of beta-BaZn2As2 was evaluated to be around 0.2 eV, which is much smaller than that of a family compound LaZnOAs (1.5 eV). Density functional theory calculation using the Heyd-Scuseria-Ernzerhof hybrid functionals supports the small band gap. (C) 2013 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.tsf.2013.10.135

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We report herein a high and isotropic critical-current density J(c) for BaFe2(As,P)(2) epitaxial films. The isotropy of J(c) with respect to the magnetic-field direction was improved significantly by decreasing the film growth rate to 2.2 angstrom/s. The low growth rate served to preferentially align dislocations along the c-axis, which work well as c-axis vortex-pinning centers. Because of the intentional introduction of effective pinning, the absolute J(c) at 9 T was larger than that obtained for other iron-based superconductors and conventional alloy superconducting wires. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4875956

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1073/pnas.1318045111

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELECTROCHEMICAL SOC INC  

A p-type oxide semiconductor, tin monoxide (SnO), is expected for high-mobility p-channel oxide thin-film transistors. In this study, we fabricated polycrystalline SnO films by three methods based on pulsed laser deposition, direct deposition at high temperatures, in-situ thermal annealing without exposure to air, and ex-situ thermal annealing after exposure to air. It was found that the crystallite orientation depends largely on the fabrication methods; i.e., the direct deposition enhanced c-axis orientation in particular at higher temperatures, and the in-situ thermal annealing induced homogeneous nucleation of non-oriented crystallites at high temperatures. Further, ex-situ thermal annealing nucleated (101)-oriented crystallites due probably to surface contamination originating from air exposure. In-plane Hall mobility was related to the film texture; i.e., the c-axis oriented films exhibited higher hole mobilities in the a-b plane while the more (101)-oriented films exhibited lower mobilities. This observation was attributed to an intrinsic nature that heavier effective hole mass along the Gamma-Z direction ([001] direction) than that of the Gamma-M direction ([110] direction), originating from strong anisotropy of the layered crystal structure of SnO. The on-state currents of SnO TFTs fabricated by 300 degrees C deposition or thermal annealing were explained qualitatively by the hole mobilities measured by Hall effect. (c) 2014 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.009409jss

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.4874609

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ic401487q

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：International Display Workshops  

We have developed 3-D stacked complementary TFT devices using n-Type u-IGZO and p-Type F8T2 TFTs on PET substrates. We confirm correct input-output characteristics of inverter circuits. Particularly in this presentation, we compare n-Type a-IGZO, p-Type F8T2, stacked complementary, and sided complementary inverters.

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.88.140503

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1367-2630/15/7/073019

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/TASC.2012.2234935

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.87.064504

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2109/jcersj2.120.447

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Institute of Physics  

DOI： 10.1063/1.4744983

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

An operation model for an amorphous In-Ga-Zn-O (a-IGZO) based thin film transistor (TFT) is studied. The model is not based on the exponential tail states employed in hydrogenated amorphous Si (a-Si:H) TFT, but on a power function of the carrier density which is observed in the TFT and Hall mobilities of a-IGZO. A 20 numerical simulator employing this model reproduced current-voltage characteristics under on operation of coplanar homojunction a-IGZO TFTs. Although the mathematical expression of the mobility is similar to the field effect mobility of a-Si:H TFT, the present model explains the temperature dependence of the on characteristics of a-IGZO TFT. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2011.10.060

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE SA  

The stability of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) was investigated focusing on the effects of passivation layer materials (Y2O3, Al2O3, HfO2, and SiO2) and thermal annealing. Positive bias constant current stress (CCS), negative bias stress without light illumination (NBS), and negative bias light illumination stress (NBLS) were examined. It was found that Y2O3 was the best passivation layer material in this study in terms of all the stability tests if the channel was annealed prior to the passivation formation (post-deposition annealing) and the passivation layer was annealed at &gt;= 250 degrees C (post-fabrication annealing). Post-fabrication thermal annealing of the Y2O3 passivation layer produced very stable TFTs against the CCS and NBS stresses and eliminated subgap photoresponse up to the photon energy of 2.9 eV. Even for NBLS with 2.7 eV photons, the threshold voltage shift is suppressed well to -4.4 V after 3 h of test. These results provide the following information: (i) passivation removes the surface deep subgap defects in a-IGZO and eliminates the subgap photoresponse, but (ii) the bulk defects in a-IGZO should be removed prior to the passivation process. The Y2O3-passivated TFT is not only stable for these stress conditions, but is also compatible with high-frequency operation with the current gain cut-off frequency of 91 kHz, which is consistent with the static characteristics. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2011.10.068

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Royal Society of Chemistry  

DOI： 10.1039/c2jm14966d

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.tsf.2011.10.066

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掲載種別：研究論文（学術雑誌）  

March 2012

DOI： 10.1109/LED.2011.2179111

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掲載種別：研究論文（学術雑誌）  

Sept. 2012

DOI： 10.1016/j.sse.2012.04.037

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.mseb.2011.12.009

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.85.140516

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0953-2048/25/8/084015

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掲載種別：研究論文（学術雑誌）  

DOI： 10.3164/jcbn.10-41

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELECTROCHEMICAL SOC INC  

The photovoltaic properties and electronic structures of amorphous In-Ga-Zn-O (a-IGZO)/p-type Si heterojunctions were investigated. An optimized solar cell with a conversion efficiency of 5.3% was obtained by vacuum annealing at 300 degrees C. The short circuit current was 28.1 mA.cm(-2), which approaches the theoretical limit without an electron back reflector. The open circuit voltage (V(oc)) was 0.31 V, which was limited by the built-in potential of 0.39 V. This result combined with hard x-ray photoemission spectroscopy provided the electron affinity and ionization potential of a-IGZO, indicating the low V(OC) was controlled by the deep conduction band bottom of a-IGZO. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3595741] All rights reserved.

DOI： 10.1149/1.3595741

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掲載種別：研究論文（学術雑誌）  

Aug. 2011

DOI： 10.1063/1.3633100

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/ncomms1419

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3599844

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ja107042r

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.mseb.2010.02.007

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.mseb.2009.12.018

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.mseb.2010.01.004

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.tox.2009.12.015

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3455072

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1063/1.3458799

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.mseb.2010.01.051

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nimb.2009.03.043

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nimb.2009.03.056

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

DOI： 10.1103/PhysRevB.77.224431

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

DOI： 10.1103/PhysRevB.77.214515

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

DOI： 10.1103/PhysRevB.76.195325

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掲載種別：研究論文（学術雑誌）  

Effects of O 2- or OH - ion incorporation on the cage geometry in 12CaO·7Al 2O 3 (C12A7) crystals are examined by the maximum entropy method (MEM)/Rietveld analyses of synchrotron powder X-ray diffraction data. Presence of an extraframework anion in a cage causes inward displacements of two Ca 2+ ions axially coordinating to the anion. The OHion locates at the cage center and induces smaller symmetric displacements of the two Ca 2+ ions, while the O 2- ion likely locates on off-axis positions and induces larger asymmetric Ca 2+ ion displacements. Copyright © 2007 The Chemical Society of Japan.

DOI： 10.1246/cl.2007.902

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1149/1.2789296

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1149/1.2388737

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掲載種別：研究論文（学術雑誌）  

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The device characteristics of thin-film transistors (TFTs) having amorphous In-Ga-Zn-O channel layers with various chemical compositions were studied by using combinatorial synthesis techniques. The In-Ga-Zn-O films were prepared by a radio-frequency magnetron sputtering method at room temperature in mixed-gas atmosphere of argon and oxygen. The TFT libraries enabled us to systematically survey the device characteristics of the TFTs in a wide compositional range of channel materials. It is found that the TFT characteristics are very sensitive to the chemical composition ratio of In:Ga:Zn and depend also on the oxygen partial pressure during deposition. Some devices exhibited good performance of the field-effect mobility of ∼10 cm2V-1sec -1 and on-to-off current ratio of ∼108. © 2006 Materials Research Society.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Electronic and optical properties of widegap oxychalcogenides, LaCuOCh (Ch = chalcogen) and La2CdO2Se2, are reviewed with a focus on those relevant to their layered crystal structures, including high hole mobility, degenerate p-type conduction, room temperature exciton, and large third order optical nonlinearity. In particular, the widegap p-type metallic conduction was realized in Mg-doped LaCuOSe: the first demonstration among any class of widegap materials including GaN: Mg. Furthermore, we demonstrate the room temperature operation of a blue light-emitting diode using a pn hetero-junction composed of a LaCuOSe epilayer and an n-type amorphous InGaZn5O8. Those results strongly suggest that a series of the layered oxychalcogenides are applicable to the light-emitting layers in opto-electronic devices that operate in the ultraviolet-blue region as well as to transparent p-type conductors. (c) 2006 WILEY-VCH Verlag GmbH & Co. KG&A, Weinheim.

DOI： 10.1002/pssa.200669665

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society  

DOI： 10.1021/ja063355c

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

DOI： 10.1016/j.jssc.2006.02.031

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1149/1.2210669

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.nimb.2004.01.206

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1109/LED.2003.815006

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/S0168-583X(03)01071-1

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JJAP.42.L625

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掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/S0040-6090(03)01170-2

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記述言語：英語  

DOI： 10.1016/j.tsf.2009.10.132

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Amorphous oxide semiconductors (AOSs) are expected for alternative channel materials in thin-film transistors owing to their large electron mobilities. While, it is known that AOSs exhibit peculiar electron transport properties. Definite Hall voltages are observed even for mobilities &lt; 0.2 cm(2)/V s, which correspond to a very short mean free path (MFP) of 0.008 nm. Furthermore, Hall mobility increases with increasing the donor density. This paper reports that a percolation conduction model explains them; quantitative analyses based on the Boltzmann&apos;s transport theory prove that carriers within the potential barriers have large MFPs of 0.5-1 nm. The percolation model also explains variable-range-hoppinglike and weak-localizationlike behaviors.

DOI： 10.1063/1.3364131

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

Atomically flat single-crystalline thin films or ScAlMgO4 (SCAM) were fabricated on yttria-stabilized zirconia (YSZ) (111)substrates by reactive solid-phase epitaxy using an ablation ceramic target with an optimized chemical composition. Owing to the good lattice matching, the SCAM layers enhanced two-dimensional growth of ZnO epitaxial films, suppressed the formation of threading dislocations at step edges, and provided larger Hall mobilities than those of ZnO films on YSZ and Al2O3 single-crystal substrates especially at low deposition temperatures &lt; 700 degrees C. The ZnO films exhibited Hall voltage anomaly at temperatures &lt; 140 K, which is explained by a two-layer model with a degenerated layer.

DOI： 10.1021/cg900616c

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

Photoresponse was investigated for an amorphous oxide semiconductor, In-Ga-Zn-O, by the steady-state photoconductivity (SSPC) method All the films exhibited extremely slow reversible photoresponses. Analysis of the transient photocurrent at varied temperatures provided similar activation energies of similar to 0.5 eV for both the time constants and the photoconductivity. Mobility-lifetime (mu tau) products were estimated from the photoconductivity spectra measured at the sweep rate of 2 nm/s, which monotonically increased with increasing dark conductivity sigma(D) (i e the Fermi level E-F becomes shallower) The obtained mu tau values are larger than those of hydrogenated amorphous silicon even if the E-F dependence is considered (C) 2009 Elsevier B.V. All rights reserved

DOI： 10.1016/j.tsf.2009.10.129

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記述言語：英語   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Epitaxial growth and electron doping of 12CaO center dot 7Al(2)O(3) (C12A7) and 12SrO center dot 7Al(2)O(3) (S12A7) are reported. The C12A7 films were prepared on Y3Al5O12 (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 parallel to (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 Minis provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, Suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2009.11.031

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記述言語：英語  

DOI： 10.1016/j.jssc.2009.11.031

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DOI： 10.1038/asiamat.2010.5

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記述言語：日本語   出版者・発行元：金属鉱山会  

CiNii Books

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記述言語：英語   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

High critical current densities J(c) of 4 MA/cm(2) at 4 K were obtained in Co-doped BaFe2As2 (BaFe2As2:Co) epitaxial films grown directly on (La, Sr)(Al, Ta)O-3 substrates by pulsed laser deposition. Use of a highly pure target and improvement of film homogeneity were the critical factors to achieve the high J(c). The improved BaFe2As2:Co epitaxial films contained almost no Fe impurity and showed high crystallinity (crystallite tilt angle Delta omega = 0.5 degrees and twist angle Delta phi = 0.5 degrees) and a sharp superconducting transition with a width of 1.1 K. It is considered that these improvements resulted in the enhanced superconducting properties comparable to those of single crystals. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/APEX.3.063101

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DOI： 10.1038/asiamat.2010.5

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DOI： 10.1063/1.3364131

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記述言語：英語   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Electronic structures and carrier transport mechanisms in disordered oxide semiconductors, crystalline InGaO3 ZnO)(m) (m = 1, 5) (c-IGZO) and amorphous InGaZnO4 (a-IGZO), are examined based on a percolation conduction model. Donor levels (E-d) and densities (N-D) are estimated by numerical calculations of free electron densities (n(e)) obtained by Hall measurements. It shows that the donor levels are rather deep, similar to 0.15 eV for c-IGZO and similar to 0.11 eV for a-IGZO. This analysis indicates that use of a simple analytical relation of n(e) proportional to exp(-E-d/2kT) can not always be used to estimate E-d and N-D even for a low n(e) film because the film can be in the saturation regime at room temperature if E-d and N-D are small, which is actually the case for a-IGZO. The temperature dependences of electron mobilities are analyzed using an analytical equation of the percolation conduction model, which reveals that distributed potential barriers exist above mobility edges in IGZO with average heights 30-100 meV and distribution widths 5-20 meV, which depend on atomic structure and deposition condition of IGZO films. High-quality a-IGZO films have the lowest potential barriers among the IGZO films examined, in spite that a-IGZO has a more disordered amorphous structure than c-IGZO have. It is explained by the partly disordered structure of c-IGZO.

DOI： 10.1109/JDT.2009.2022064

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記述言語：英語  

Electronic structures and carrier transport mechanisms in disordered oxide semiconductors, crystalline InGaO3(ZnO)m (m = 1, 5) (c-IGZO) and amorphous InGaZnO4 (a-IGZO), are examined based on a percolation conduction model. Donor levels (Ed) and densities (N D) are estimated by numerical calculations of free electron densities (ne) obtained by Hall measurements. It shows that the donor levels are rather deep, ∼ 0.15 eV for c-IGZO and ∼ 0.11 eV for a-IGZO. This analysis indicates that use of a simple analytical relation of ne (-Ed/2kT) can not always be used to estimate Ed and N D even for a low ne film because the film can be in the saturation regime at room temperature if Ed and ND are small, which is actually the case for a-IGZO. The temperature dependences of electron mobilities are analyzed using an analytical equation of the percolation conduction model, which reveals that distributed potential barriers exist above mobility edges in IGZO with average heights 30100 meV and distribution widths 520 meV, which depend on atomic structure and deposition condition of IGZO films. High-quality a-IGZO films have the lowest potential barriers among the IGZO films examined, in spite that a-IGZO has a more disordered amorphous structure than c-IGZO have. It is explained by the partly disordered structure of c-IGZO. © 2006 IEEE.

DOI： 10.1109/JDT.2009.2022064

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) with a coplanar homojunction structure are demonstrated. The coplanar source and drain regions made of a-IGZO were formed by depositing a hydrogenated silicon nitride (SiNX:H) layer onto the a-IGZO layer. The a-IGZO regions on which the SiNX:H layer was directly deposited showed the low resistivity of 4.7 x 10(-3) Omega cm and degenerated conduction. The fabricated TFT showed excellent transfer and output characteristics with a field-effect mobility of 11 cm(2) V-1 s(-1), a subthreshold swing of 0.17 V decade(-1,) and an on-to-off current ratio larger than 1 x 10(9). The width-normalized source-to-drain resistance (R-sd W) calculated using a channel resistance method was 51 Omega cm. This TFT also showed good stability over environment change and under electrical stress. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2009.01.165

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記述言語：英語   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

The epitaxial growth of Fe-based superconductors such as Co-doped SrFe2As2 (SrFe2As2:CO) was reported recently, but has still insufficient properties for a device application because they have rough surfaces and are decomposed by reactions with water vapor in an ambient atmosphere. This paper reports that epitaxial Films of Co-doped BaFe2As2 grown at 700 degrees C show the onset superconducting transition temperature of similar to 20 K. The transition is sharper than those observed on the SrFe2As2:Co films, which would originate from their improved crystallinity. These films also have atomically-flat surfaces with step-and-terrace structures and exhibit chemical stability against exposure to water vapor. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2009.10.001

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記述言語：英語  

Tin monoxide (SnO) is a stable p-type oxide semiconductor. This paper reports electrical properties, electronic structures, and thin-film transistors (TFTs) of SnO. Epitaxial films were fabricated by pulsed laser deposition. The Hall mobility and he hole density of the epitaxial films were 2.4 cm 2 V -1 s -1 and 2.5×10 17, respectively. X-ray photoelectron spectroscopy (PES) indicated that the closed-shell 5s 2 orbitals of Sn 2+ ions heavily contribute to the hole conduction path in SnO. Top gate type TFTs (W/L=300/50 μm) employing 20 nm thick SnO channels exhibited field-effect mobilities μ sat =0.7 cm 2V -1 s -1 and μ lin =1.3 cm 2 V -1 s -1, which are larger by two orders of magnitude than those reported for pchannel oxide TFTs to date. On/off current ratios werẽ10 2 and subthreshold voltage swings (S) ̃7 V/decade. The parameters required for TFT simulations were estimated by ultraviolet PES and first-principles calculations. The TFT simulations indicated that subgap hole trap density in the SnO channel is&gt
10 19 cm -3, which limits the TFT mobilities and the S values. © 2009 WILEY-VCH Verlag GmbH &amp
Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200881792

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

Tin monoxide (SnO) is a stable p-type oxide semiconductor. This paper reports electrical properties, electronic structures, and thin-film. transistors (TFTs) of SnO. Epitaxial films were fabricated by pulsed laser deposition. The Hall mobility and the hole density of the epitaxial films were 2.4 cm(2) V(-1) s(-1) and 2.5 x 10(17), respectively. X-ray photoelectron spectroscopy (PES) indicated that the closed-shell 5s(2) orbitals of Sn(2+) ions heavily contribute to the hole conduction path in SnO. Top gate type TFTs (W/L = 300/50 mu m) employing 20 nm thick SnO channels exhibited field-effect mobilities mu(sat) = 0.7 cm(2) V(-1) s(-1) and mu(lin) = 1.3 cm(2) V(-1) s(-1), which are larger by two orders of magnitude than those reported for p-channel oxide TFTs to date. On/off current ratios were similar to 10(2) and subthreshold voltage swings (S) similar to 7 V/decade. The parameters required for TFT simulations were estimated by ultraviolet PES and first-principles calculations. The TFT simulations indicated that subgap hole trap density in the SnO channel is &gt; 10(19) cm-3, which limits the TFT mobilities and the S values. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssa.200881792

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

We grew epitaxial (110) Cu(2)O films on (110) MgO substrates toward high-mobility p-channel oxide thin-film transistors (TFTs). The (110) Cu(2)O films exhibited high Hall mobilities similar to 90 cm(2)(Vs)(-1) comparable to those of high-quality single-crystals, which were obtained in a narrow growth condition for 650 nm-thick films. TFTs using the epitaxial (110) Cu(2)O channels exhibited p-channel operation, but the field-effect mobilities and the on-to-off drain current ratio were far from satisfaction (similar to 0.04 cm(2)(Vs)(-1) and similar to 2, respectively). In order to investigate the origin of the poor mobility, the films were subjected to post-deposition annealing under various oxygen partial pressures (P(O2-A) = 0.65-10(-3) Pa). Optical measurements revealed that subgap states exist in all the films and their amounts were increased by post-deposition annealing irrespective of P(O2-A). The subgap density of states estimated by the optical analyses are consistent roughly with that estimated from the TFT mobility. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssa.200881795

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記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

It has been considered that FeAs-based high-transition temperature (high-T-c) superconductors need electron or hole doping by aliovalent-ion substitution or large off stoichiometry in order to induce superconductivity. We report that exposure of undoped SrFe2As2 epitaxial thin films to water vapor induces a superconducting transition. These films exhibit a higher onset T-c (25 K) and larger magnetic field anisotropy than those of cobalt-doped SrFe2As2 epitaxial films, suggesting that the mechanism for the observed superconducting transition differs from that of the aliovalent-ion-doped SrFe2As2. The present finding provides an interesting approach to induce superconductivity with a higher T-c in FeAs-based superconductors.

DOI： 10.1103/PhysRevB.80.052501

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Threshold voltage (V(th)) stability was examined under constant current stress for a-In-Ga-Zn-O thin film transistors (TFTs) deposited at room temperature and annealed at 400 degrees C in dry or wet O(2) atmospheres. All the TFTs exhibited positive V(th) shifts (Delta V(th)) and the Delta V(th) value was reduced by the thermal annealing to &lt; 2 V for 50 h. TFT simulations revealed that the Delta V(th) for the annealed TFTs is explained by increase in deep charged defects. Large Delta V(th) over 10 V and deterioration in subthreshold voltage swing were observed in the unannealed TFTs, which are attributed to the increase in shallow trap states. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3159831]

DOI： 10.1063/1.3159831

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記述言語：英語  

DOI： 10.1063/1.3159831

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記述言語：英語  

This paper discusses an optical model and subgap electronic states for a representative amorphous oxide semiconductor, InGaZnO 4 (a-IGZO). Parameterized optical models were de veloped based on the Tauc-Lorentz model combined with a Lorentz-type oscillator. The measured optical absorption spectra exhibit nearly linear dependences on photon energy (E) between 3 eV &lt
E &lt
5 eV, which requires the transition energies in the Tauc -Lorentz model (E 0,TL) being around 4 eV. The optimized parameters for the fixed E 0,TL of 3.7 eV are provided for four different a-IGZO films with root-mean square errors less than 1%. Formation energies of crystalline IGZO, stoichiometric a-IGZO, oxygen deficient a-IGZO and their constituent oxides were calculated by the density func tional theory using the local density approximation (LDA) and generalized gradient approximation with PBE96 func tionals (PBE). PBE gives larger unit cell volumes at the ground states and better agreement in the formation energies than LDA does. The formation energies of an oxygen defi ciency in a-IGZO were calculated to be 3.2-3.5 eV. The cal culated electronic structures of stoichiometric a-IGZO models exhibit somewhat large dispersions for conduction bands (CB), which are not largely affected by the disordered struc ture in a-IGZO, while the dispersions of the valence bands (VBs) are very small, unlike the crystalline IGZO, showing that a-IGZO have strongly localized states at the VB maxi mums (VBMs). Oxygen-deficient a-IGZO models showed that oxygen deficiencies form both a deep localized state at 0.4-1 eV above VBM and a shallow donor state depending on local atomic configurations. An oxygen deficiency that forms a deep state breaks the dispersion of the CB, which could be an origin of the subgap states observed near CB. © 2009 WILEY-VCH Verlag GmbH &amp
Co. KQaA.

DOI： 10.1002/pssa.200881303

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記述言語：英語  

DOI： 10.1002/pssa.200881303

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high Superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard Pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and Succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe2As2. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.03.026

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Materials in In-Ga-Zn-O system are promising candidates for channel layers of high- performance thin-film transistors (TFTs). We investigated the atomic arrangements and the electronic structures of crystalline InGaZnO(4) containing point defects such as oxygen vacancy (V(O)), interstitial hydrogen (H(i)), and interstitial oxygen (O(i)) by density functional theory (DFT) using a plane-wave pseudopotential method. The calculations for the atomic structure relaxation suggest that Hi bonds to a lattice oxygen (O(O)), and Oi occupies a split interstitial site [O(i) (split)] forming a chemical bond with O(O) which is similar to O(2) molecule, or Oi occupies an octahedral interstitial site [O(i)(oct)]. The electronic structure calculations reveal that V(O) forms fully occupied states around the middle of the DFT band gap, while Hi does not form a defect level in the band gap but raises the Fermi level above the conduction band minimum. O(i)(split) forms fully occupied states above the valence band maximum of the defect-free model (VBM(0)), while O(i)(oct) forms both occupied and unoccupied states above the VBM(0). It is thus suggested that V(O) and O(i)(split) are electrically inactive for electrons but work as hole traps, Hi acts as a donor, and O(i)(oct) is electrically active, trapping both electrons and holes. These observations imply that VO and O(i)(split) do not but Hi and O(i)(oct) influence electrical properties of the n-channel TFTs based on the In-Ga-Zn-O semiconductor materials. (C) 2009 American Institute of Physics. [DOI:10.1063/1.3089232]

DOI： 10.1063/1.3089232

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Electronic and magnetic properties of a layered compound LaMnPO are examined in relation to a newly discovered iso-structural superconductor LaFeAs(P)O. Neutron diffraction measurements, together with temperature dependent magnetic susceptibility, clarify that LaMnPO is an antiferromagnet at least up to 375 K. The spin moment of a Mn ion is determined to be 2.26 mu(B) at room temperature, and the spin configuration is antiparallel in the Mn-P plane and parallel between the Mn-P planes, which is rather different from that of LaFeAsO. Optical absorption spectra, photoemission spectra, and temperature dependent electrical conductivity indicate that LaMnPO is a semiconductor. Furthermore, nominally undoped LaMnPO exhibits n-type conduction while the conduction type is changed by doping of Cu or Ca to the La sites, indicating that LaMnPO is a bipolar conductor. Density functional calculation using the GGA+U approximation supports the above conclusions; the electronic band structure has an open band gap and the antiferromagnetic spin configuration is more stable than the ferromagnetic one. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3124582]

DOI： 10.1063/1.3124582

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記述言語：英語  

DOI： 10.1016/j.mseb.2008.11.042

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

12CaO center dot 7Al(2)O(3) (C12A7) is a typical band insulator, but may be converted to a metallic conductor C12A7:e(-) by electron-doping via removal of free oxygen ions sitting in the subnanometer-sized cages as the counter ions. Also, C12A7 is known as a fast oxygen ion conductor. These unique features let us expect that it would be possible to dope electrons to C12A7 by removing the free oxygen ions by an external electric field. in this Study, we fabricated C12A7/C12A7:e(-) stacking devices and examined their current-voltage characteristics. The thickness of the top C12A7 layer was controlled by low-temperature oxidation with an aid of an optical model analysis of spectroscopic ellipsometry. We found that the C12A7/C12A7:e(-) devices exhibited a bistable resistance switching effect with an on-to-off resistance ratio of similar to 10(2) and operated as a resistive random access memory. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2008.11.042

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

A homologous series compound ScAlO3(MgO) (SCAM) has a superior lattice matching as small as similar to 1.4% in a-axis with GaN. This paper reports an efficient fabrication process of a single-crystalline SCAM buffer layer on a (1 1 1) yttria-stabilized zirconia (YSZ) substrate using pulsed laser deposition (PLD). A 10-nm thick ZnO epitaxial layer was used to induce solid-phase epitaxial growth of an amorphous (a-) SCAM layer formed at room temperature on (1 1 1) YSZ. It was found that the addition of excess Sc2O3 and ZnO to a SCAM target used for PLD was needed to obtain single-crystalline SCAM films with atomically flat terraces-and-steps surfaces. The resulting single-crystalline SCAM films were examined as buffer layers to grow GaN by molecular beam epitaxy with a plasma nitrogen source. The GaN films were grown epitaxially on the SCAM/YSZ substrates with the epitaxial relationship of [0 0 0 1] GaN parallel to[0 0 0 1] SCAM parallel to[1 1 1] YSZ and [1 0 0] GaN parallel to [11-20] SCAM parallel to [1-10] YSZ. The SCAM buffer layers enhanced lateral growth of the GaN films owing to the good lattice matching. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2009.02.003

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Thin films of LaMnXO (X=P, As, and Sb), which are isostructural compounds of the newly discovered superconductor, LaFeAsO, were grown epitaxially on MgO(001) substrates at similar to 680 degrees C by pulsed laser deposition. Postdeposition thermal annealing at 1000 degrees C in evacuated silica glass ampoules improved the crystallinity and orientation for the LaMnPO and LaMnAsO films, but it led to the phase segregation of the LaMnSbO film. Thermopower and optical absorption measurements revealed that all the films are p-type semiconductors with indirect bandgaps from 1.0 to 1.4 eV, which are supported by density functional calculations with the GGA+U approximation. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3093685]

DOI： 10.1063/1.3093685

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

A fabrication process of coplanar homojunction thin-film transistors (TFTs) is proposed for amorphous In-Ga-Zn-O (a-IGZO), which employs highly doped contact regions naturally formed by deposition of upper protection layers made of hydrogenated silicon nitride (SiNX:H). The direct deposition of SiNX:H reduced the resistivity of the semiconductive a-IGZO layer down to 6.2x10(-3) Omega cm and formed a nearly ideal Ohmic contact with a low parasitic source-to-drain resistance of 34 Omega cm. Simple evaluation of field-effect mobilities (mu(sat)) overestimated their values especially for short-channel TFTs, while the channel resistance method proved that mu(sat) was almost constant at 9.5 cm(2) V-1 s(-1).

DOI： 10.1063/1.3112566

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記述言語：英語  

DOI： 10.1063/1.3112566

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記述言語：英語  

Optoelectronic properties and device applications of layered mixed-anion compounds such as oxychalcogenide LaCuOCh (Ch = chalcogen) and oxypnictide LaTMOPn (TM = 3d transition metal, Pn = pnicogen) are reviewed. Several distinctive functions have been found in these materials based on our original material exploration concept. Fabrication of high-quality epitaxial films of LaCuOCh leads to clarifying the excellent electrical and optical properties such as high hole mobility of 8 cm2/(V s) and heavy hole doping at &gt
1021 cm-3 in LaCuOSe, and sharp and tunable-wavelength photoluminescence in the solid-solution systems in LaCuOCh. In addition, a room temperature operation of a light-emitting diode is demonstrated using LaCuOSe as a light-emitting layer. These results suggest that the layered oxychalcogenides have potential for light-emitting layers as well as transparent hole-injection layers in organic/inorganic light-emitting diodes. Furthermore, by extending the material system from the copper-based oxychalcogenides to isostructural compounds, transition metal-based oxypnictides LaTMOP (TM = Fe, Ni), we have found novel superconductors, LaFeOP and LaNiOP. © 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jeurceramsoc.2008.03.016

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記述言語：英語   出版者・発行元：ELSEVIER SCI LTD  

Optoelectronic properties and device applications of layered mixed-anion compounds such as oxychalcogenide LaCuOCh (Ch = chalcogen) and oxypnictide LaT(M)OPn (T(M) = 3d transition metal, Pn = pnicogen) are reviewed. Several distinctive functions have been found in these materials based on our original material exploration concept. Fabrication of high-quality epitaxial films of LaCuOCh leads to clarifying the excellent electrical and optical properties such as high hole mobility of 8 cm(2)/(V s) and heavy hole doping at &gt;10(21) cm(-3) in LaCuOSe, and sharp and tunable-wavelength photoluminescence in the solid-solution systems in LaCuOCh. In addition, a room temperature operation of a light-emitting diode is demonstrated using LaCuOSe as a light-emitting layer. These results suggest that the layered oxychalcogenides have potential for light-emitting layers as well as transparent hole-injection layers in organic/inorganic light-emitting diodes. Furthermore, by extending the material system from the copper-based oxychalcogenides to isostructural compounds, transition metal-based oxypnictides LaT(M)OP (T(M) = Fe, Ni), we have found novel superconductors, LaFeOP and LaNiOP. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jeurceramsoc.2008.03.016

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記述言語：英語   出版者・発行元：ELECTROCHEMICAL SOC INC  

The effect of humidity on the electrical conductivity in porous and dense ceramics of Ca12Al14-xSixO32Cl2+x (x=0, 1.7, 3.4) with a mayenite structure was examined at room temperature. Surface ionic conductivity was enhanced by increasing the humidity. The sample with x=3.4, which had a porosity of 30%, exhibited the largest conductivity change of about 4 orders of magnitude over the relative humidity range of 10-90% at 25 degrees C. The presence of Cl- ions on the surface most likely enhances the formation of hydronium ions which are responsible for proton transfer in physisorbed water layers.

DOI： 10.1149/1.3032908

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DOI： 10.1016/j.jeurceramsoc.2008.03.016

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DOI： 10.1021/jp906386q

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DOI： 10.1002/pssa.200881792

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DOI： 10.1016/j.mseb.2009.02.003

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DOI： 10.1063/1.3124582

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DOI： 10.1002/pssa.200881792

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記述言語：英語  

The effect of humidity on the electrical conductivity in porous and dense ceramics of Ca12 Al14-x Six O32 Cl2+x (x=0, 1.7, 3.4) with a mayenite structure was examined at room temperature. Surface ionic conductivity was enhanced by increasing the humidity. The sample with x=3.4, which had a porosity of 30%, exhibited the largest conductivity change of about 4 orders of magnitude over the relative humidity range of 10-90% at 25°C. The presence of Cl- ions on the surface most likely enhances the formation of hydronium ions which are responsible for proton transfer in physisorbed water layers. © 2008 The Electrochemical Society.

DOI： 10.1149/1.3032908

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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

We report electrical and magnetic properties of LaTMPO (TM = Fe, Ni) under high pressures. From resistivity measurements, superconducting transition temperature T-c for LaFePO and LaNiPO increases steeply up to about 0.8 GPa, and the dT(c)/dP values are more than 4 K/GPa and 1 K/GPa, respectively. From the results of high-pressure x-ray diffraction measurements, the oxypnictide compounds show an anisotropic compression along a-axis and c-axis.

DOI： 10.1088/1742-6596/150/5/052075

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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

Undoped LaFePnO (Pn = P, As) shows metallic resistivity and a tetragonal phase at room temperature. The electrical resistivity (rho) of undoped LaFeAsO exhibits a sudden decrease around T-anom similar to 160 K with decreasing the temperature and increases with decreasing the temperatures (T) below another threshold temperature (T-min). It makes a contrast to undoped LaFePO, which shows neither of T-anom nor T-min. The T-anom corresponds to a crystallographic phase transition: undoped LaFeAsO shows an orthorhombic phase at temperatures &lt; 160 K. A positive magnetoresistance (MR = (rho-rho(0)) / rho(0)) also appears below T-anom. DFT calculations indicate that spin moment of LaFeAsO is 1.56 mu(B) / Fe in an antiferromagnetic spin configuration in a tetragonal phase, while spin moment of LaFePO is almost quenched.

DOI： 10.1088/1742-6596/150/5/052090

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DOI： 10.1021/jp906386q

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記述言語：日本語   出版者・発行元：アグネ技術センタ-  

CiNii Books

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Copper selenide, Cu(x)Se(x similar to 2), was examined as a hole-injection layer for low-temperature organic devices. Crystalline CuxSe films grown at room temperature with atomically flat surfaces exhibited metallic conduction with a high electrical conductivity of 4.5 x 10(3) S/cm, a hole concentration of 1.4 x 10(22) cm(-3), and a mobility of 2.0 cm(2)/(V s). Analysis of the free carrier absorption using the Drude model estimated the effective mass of a hole as 1.0m(e). Photoemission spectroscopy measurements of the interfaces between CuxSe and organic hole transport layers, N, N&apos;-bis(naphthalen-1-y1)-N,N&apos;]-bis(phenyl)benzidine (NPB) and copper phthalocyanine (CuPc), verified that the hole-injection barriers of these interfaces (0.4 eV for NPB and 0.3 eV for CuPc) are smaller than that of a conventional indium tin oxide (ITO) hole-injection electrode/NPB interface (0.6 eV) but are comparable to that of an ITO electrode/CuPc interface (0.3 eV). Hole-only devices using the CuxSe layer as a hole-injection anode exhibited very low threshold voltages (0.4-0.5 V) and nearly Ohmic characteristics. The NPB layer on the Cu(x)Se layer was found to be highly doped at 10(17)-10(19) cm(-3), probably due to copper diffusion, while the CuPc layer is nearly intrinsic with a doping concentration lower than 10(15) cm(-3). These results indicated that a CuxSe film combined with CuPc is a promising candidate for a low-voltage hole-injection anode or a buffer layer in low-temperature devices such as organic light-emitting diodes and thin film transistors. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3039167]

DOI： 10.1063/1.3039167

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記述言語：英語   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

Effects of the replacement of La with Ce on the electronic and magnetic properties of a layered superconductor LaFePO (T(c) = similar to 5 K) were studied. Polycrystalline samples of CeFePO, prepared by a solid-state reaction, showed metallic conduction down to 2K without exhibiting superconducting transition, although the resistivity decreased largely at temperatures below 30 K. Further, they showed an apparent positive magnetoresistance (MR) below similar to 2 K, superposed on a negative MR. Temperature dependence of magnetic susceptibility is decomposed to a temperature-sensitive Curie-Weiss component presumably due to the Ce(3+) ions with a magnetic moment of 1.98 mu(B) and a less temperature-sensitive component attributable to itinerant electrons. The magnetic interaction between Ce(3+) ions and itinerant electrons in CeFePO likely suppresses the Superconducting transition observed in LaFePO. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2008.08.011

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記述言語：英語   出版者・発行元：MATERIALS RESEARCH SOC  

This article provides a review of materials and devices of wide-bandgap oxide semiconductors based on ZnO, highlighting the nature of the chemical bond. The electronic structures of these materials are very different from those of conventional covalently bonded semiconductors, owing to the ionic nature of the chemical bonds. Therefore, one needs to design and optimize fabrication processes and structures of active devices containing such materials, taking into account the peculiar defect formation mechanisms. A variety of active devices that have clear advantages over the conventional ones have been demonstrated, for example, ultraviolet light-emitting diodes, quantum Hall devices, and transparent and flexible thin-film transistors with high electron mobility, paving the way for future applications. The reasons behind the successes identify future challenges in research on oxide semiconductors.

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Cu(2)O epitaxial films were grown for high mobility p-channel oxide thin-film transistors (TFTs). The use of a (110) MgO surface and fine tuning of a growth condition produced single phase epitaxial films with hole Hall mobilities similar to 90 cm(2) V(-1) s(-1) comparable to those of single crystals (similar to 100 cm(2) V(-1) s(-1)). TFTs using the epitaxial film channels exhibited p-channel operation although the field-effect mobilities and the on-to-off current ratio were not yet satisfactory (similar to 0.26 cm(2) V(-1) s(-1) and similar to 6, respectively).

DOI： 10.1063/1.3026539

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Roles of H(2)O addition to an annealing atmosphere were investigated for amorphous In-Ga-Zn-O thin-film transistors fabricated at room temperature. Although dry O(2) annealing improved saturation mobility (mu(sat)) and subthreshold voltage swings (S), wet O(2) annealing further improved them to mu(sat)similar to 12 cm(2)(V s)(-1) and S &lt; 0.12 V decade(-1) along with improvement of their uniformity. Desorption of OH-related species caused conductivity increase during thermal annealing at &lt; 310 degrees C. Zn-O components started to desorb at similar to 300 degrees C for the unannealed and the dry O(2) annealed films, while these were suppressed remarkably by the wet O(2) annealing.

DOI： 10.1063/1.3020714

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

The epitaxial thin films of LaFeAsO were fabricated on MgO(001) and mixed-perovskite (La,Sr)(Al,Ta)O(3)(001) single-crystal substrates by pulsed laser deposition using a Nd-doped yttrium aluminum garnet second harmonic source and a 10 at. % F-doped LaFeAsO disk target. Temperature dependences of the electrical resistivities showed no superconducting transition in the temperature range of 2-300 K and were similar to those of undoped polycrystalline bulk samples. The transmittance spectrum exhibited a clear peak at similar to 0.2 eV, which is explained by ab initio calculations. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2996591]

DOI： 10.1063/1.2996591

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

A new synthetic route via a solid-state reaction, the crystal Structure of 12SrO center dot 7Al(2)O(3) (S(12)A(7)) incorporated with OH- ions, and the formation of oxygen radical anions in S12A7 have been examined. Investigations using X-ray powder diffraction and thermogravimetric and evolved gas combined analyses demonstrate that homogenization promoted by molten Sr(OH)(2) hydrates and the presence of Sr-hydrogarnet precursors play crucial roles in the formation of S(12)A(7). Rietveld analyses confirm the lattice framework of S(12)A(7) has a structure identical to that of the nanoporous crystal 12CaO center dot 7Al(2)O(3) (C(12)A(7), a mayenite structure) and demonstrate that two Sr2+ ions (pole Sr2+ ions) on the S-4 axis of a cage displace toward the cage center owing to the accommodation of an OH- ion. An electron paramagnetic resonance study demonstrates that oxygen radical anions, O-2(-) and O-, are generated in the cages with concentrations on the order of 10(20) cm(-3) each by oxygen annealing. From the g-values observed at 77 K, the oxygen radical anions are interpreted as being sandwiched between the two pole Sr2+ ions rather than adsorbed on one side.

DOI： 10.1021/cm800666p

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記述言語：英語  

DOI： 10.1021/cm800666p

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記述言語：英語   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

Superconducting epitaxial films of Fe-based layered arsenide, Co-doped SrFe2As2, were grown at 700 degrees C on mixed perovskite (La,Sr)(Al,Ta)O-3(001) single-crystal substrates by pulsed-laser deposition. Both the epitaxial film and an (001)-oriented film grown at 600 degrees C exhibited superconducting transitions at similar to 20 K. The zero-resistance states of the epitaxial film were sustained under a magnetic field (H) of 9 T at 9 K when H was parallel to the c-axis, while they were sustained at higher temperatures up to 10 K for H parallel to the a-axis. This is the first demonstration of superconducting thin films of FeAs-based new superconductors. (c) 2008 The Japan Society of Applied Physics

DOI： 10.1143/APEX.1.101702

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

LaCuOSe:Mg is a wide-gap p-type semiconductor with a high concluctivity and a large work function. Potential of LaCuOSe:Mg as a transparent hole-injection electrode of organic light-emitting diodes (OLEDs) was examined by employing N,N'-diphenyl-N,N'-bis (1,1'-biphenyl)-4,4'-diamine (NPB) for a hole transport layer. Photoemission spectroscopy revealed that an oxygen plasma treated surface of LaCuOSe:Mg formed a hole-injection barrier as low as 0.3 eV, which is approximately a half of a conventional ITO/NPB interface. Hole-only devices composed of a LaCuOSe:Mg/NPB/Al structure showed a low threshold voltage similar to 0.2 V and high-density current drivability of 250 mA cm(-2) at 2 V, which is larger by two orders of magnitude than that of ITO/NPB/Al devices. These results demonstrate that LaCuOSe:Mg has great potential as an efficient transparent anode for OLEDs and other organic electronic devices. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2008.03.004

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

Electron-doped 12CaO center dot 7Al(2)O(3) (C12A7) nanowires (NWs) were fabricated by two approaches. First, spatially selective electron doping of C12A7 films was examined by using a chemical method specific to C12A7. However, the conductive NW was not formed due to diffusion of oxygen in the C12A7 films to the conductive area. Secondly, a combination of dry etching and electron doping was examined. NWs with conductivities similar to 6 S/cm at 300 K were successfully fabricated by this method. The temperature dependence of the conductivity in the NWs exhibited almost degenerated conduction down to 5 K. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200778901

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記述言語：英語   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Rietveld analysis of the powder X-ray diffraction of a new layered oxyarsenide, LaNiOAs, which was synthesized by solid-state reactions, revealed that LaNiOAs belongs to the tetragonal ZrCuSiAs-type structure (P4/nmm) and is composed of alternating stacks of La-O and Ni-As layers. The electrical and magnetic measurements demonstrated that LaNiOAs exhibits a superconducting transition at 2.4 K, and above this, LaNiOAs shows metallic conduction and Pauli paramagnetism. The diamagnetic susceptibility measured at 1.8 K corresponded to similar to 20% of perfect diamagnetic susceptibility, substantiating that LaNiOAs is a bulk superconductor. (C) 2008 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2008.04.033

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記述言語：英語  

DOI： 10.1002/pssa.200778901

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

Transparent amorphous oxide semiconductors (TAOS) such as a-InGaZnO4 are expected to be applied for channels of low-temperature high-mobility thin-film transistors (TFTs). This paper presents the fabrication and characteristics of amorphous Sn-Ga-Zn-O (a-SGZO) channel TFTs. Bottom-gate TFTs were fabricated using as-deposited and annealed a-SGZO channels on a-SiO2/n(+)-Si wafers. Contrary to a-InGaZnO4 channel TFTs, the device performances of the as-deposited channel TFTs were very poor, e.g., on-currents (4.) were &lt; 10(-7) A and on/off current ratios (R-on/off) were &lt; 10(1). The TFTs using channels annealed at 500 degrees C showed good performances such as mu sat 1.8 cm(2) V-1 s(-1). Optical measurements indicate that the improvement is accompanied by a reduction ofthe density of subgap states. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200778908

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/pssa.200778936

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

The compositional dependence of sputter-deposited Zn-In-O (ZIO) film properties and the TFT performance were studied by means of a combinatorial technique. Both the characteristics of ZIO TFTs and the ZIO film properties are very sensitive to the Zn:In ratio. The best TFT performances are obtained at Zn:In similar to 60:40 at%, where the saturation mobility (mu(sat)), subthreshold swing (S.S.), on-off current ratio (I-on/I-off), and threshold voltage (V-th) are 26.5 cm(2)/Vs, 0.24 V/dec., 10(10), and +2 V, respectively. The TFT characteristics speak at this compositional ratio. Specifically, mu(sat), I-on/I-off and V-th reach maximum, while S.S. reaches minimum at this ratio. The air stability of ZIO-TFTs was also examined for active channel layers with different Zn:In ratios, which clarified that the TFTs with high stability are obtained around the same composition ration where the best characteristics are obtained. It was confirmed by X-ray diffraction and transmission electron microscopy that the ZIO films with this composition ratio have amorphous structure. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200778909

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

Electronic structures and carrier transport properties were studied based oil ab-initio calculations for Au/ZnO/Au and Mg/ZnO/Mg two-probe models, Quantum-mechanically stable structures were obtained by density functional calculations. Electron transmission spectra and current-voltage characteristics were calculated based on a non-equilibrium Green function method with the relaxed structures. It was found that the electronic structures of the idealized models were a Schottky contact for the Au/ZnO/Au interface and an ohmic contact for the Mg/ZnO/Mg interface. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200778850

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

Copper-based chalcogenide thin films deposited at room temperature were examined for exploring an active layer material for a p-channel thin film transistor (TFT) fabricable at room temperature. The electrical conductivities of chalcopyrite and simple copper chalcogenide thin films were controlled by introducing hydrogen sulfide and oxygen gases, respectively, during the film deposition. However, no current modulation by gate bias was observed in fabricated TFTs. Optical absorption spectra showed intense subgap absorptions, and these subgap states are thought to pin the Fermi levels. Although these copper-based chalcogenides did not work as TFT channels, we found that simple copper chalcogenides deposited under a high vacuum showed p-type degenerate conduction with a high conductivity up to 7.3 x 10(3) S/cm and a reasonably large work function of similar to 4.7 eV. These properties are rather favorable for a hole injection layer of flexible electronic devices and suggest a promising application as an anode layer in organic light emitting devices. 0 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.200778906

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

Specific contact resistances between an amorphous oxide semiconductor, In-Ga-Zn-O, and various metallic electrodes, Ag, Au, In, Pt, Ti, polycrystalline indium tin oxide (ITO) and amorphous indium zinc oxide (a-IZO), were examined. All the contacts except for An and Pt showed linear current-voltage characteristics, while Au and Pt did Schottky contacts. Low contact resistances &lt; 10(-4) Omega cm(2) were obtained for the Ag, In, Ti, ITO and a-IZO contacts, and there is a trend that the contact resistance decreases with decreasing the work function of the metallic electrode. The performances of thin film transistors using ITO and Ti for source and drain contacts were better than that using the Schottky Au contacts. It was also found that the Ti contacts have a large distribution in the contact resistance, suggesting that a higher reproducibility process should be employed when reactive metals are used for an electrical contact to an oxide semiconductor. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.tsf.2007.10.051

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

This paper reports that among known p-type oxide semiconductors, tin monoxide (SnO) has a high hole mobility and produces good p-type oxide thin-film transistors (TFTs). Device-quality SnO films were grown epitaxially on (001) yttria-stabilized zirconia substrates at 575 degrees C by pulsed laser deposition. These exhibited a Hall mobility of 2.4 cm(2) V(-1) s(-1) at room temperature. Top-gated TFTs, using epitaxial SnO channels, exhibited field-effect mobilities of 1.3 cm(2) V(-1) s(-1), on/off current ratios of similar to 10(2), and threshold voltages of 4.8 V.

DOI： 10.1063/1.2964197

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

Single-crystalline thin films of ScAlMgO4 (SCAM) were fabricated on YSZ (I 11) substrates by reactive solid-phase epitaxy (R-SPE) using ScGaO3(ZnO)(m) (SGZO) single-crystalline buffer layers, which suppress interface reactions between the SCAM layers and the YSZ substrates. First, post-annealing of the SCAM layers fabricated by the R-SPE process was examined. When annealing temperature was raised to &gt; 1200 degrees C, the formation of a spinel MgAl2O4 phase was observed. This is due probably to out-diffusion of Sc ions from the SCAM layers to the YSZ substrates. By introducing an SGZO buffer layer, a single-phase SCAM layer with a step-and-terrace surface was obtained by annealing at 1450 degrees C without the spinel formation. The SCAM layer was grown heteroepitaxially with an epitaxial relationship of (000 1)SCAM // (111)ysz and 010)(SCAM) // (110)ysz. Atomically flat surfaces were eventually formed by chemical-mechanical polishing. The SCAM layer was applied to a lattice-matched buffer layer for the growth of ZnO film, leading to marked lateral growth of ZnO domains. (C) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.tsf.2007.10.049

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記述言語：英語   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

Analogous to cuprate high-T-c superconductors, a NiP-based compound system has several crystals in which the Ni-P layers have different stacking structures. Herein, the properties of BaNi2P2 are reported. BaNi2P2 has an infinite-layer structure, and shows a superconducting transition at similar to 3 K. Moreover, it exhibits metallic conduction and Pauli paramagnetism in the temperature range of 4-300 K. Below 3 K, the resistivity sharply drops to zero, and the magnetic susceptibility becomes negative, while the volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reaches similar to 100 vol.% at 1.9 K. These observations substantiate that BaNi2P2 is a bulk superconductor. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2008.05.010

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記述言語：英語  

DOI： 10.1016/j.tsf.2007.10.051

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

A p-type transparent oxide semiconductor, CuGaO2, was grown epitaxially on (111) single-crystalline yttria-stabilized zirconia (YSZ) substrates by pulsed laser deposition (PLD). Single-phase epitaxial films were obtained in narrow conditions: i.e. 725 &lt;= T-s &lt;= 780 degrees C at PO2 = 6 Pa, and 3 Pa &lt;= PO2 &lt;= 6 Pa at T-s =750 degrees C. The electrical conductivity of the as-deposited films was controlled from 3.3x 10(-5) S.cm(-1) to 1.7 x 10(-2) S center dot cm(-1) by increasing the oxygen partial pressure from 3 to 6.5 Pa. The hole concentration and Hall mobility of the most conductive film were 5x10(17) cm(-3) and 0.2 cm(2).V-1-s(-1), respectively. Estimated from the conductivity, the hole concentration was controlled from similar to 10(14) cm(-3) to similar to 10(17) cm(-3) by the oxygen partial pressure. Post-annealing at 1215 degrees C smoothed the films surface to 0.56 nm in the root-mean-squares roughness and increased the Hall mobility to 0.8 cm(2) V-1 center dot s(-1), which is the largest value among CuGaO2 films reported to date. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2007.10.072

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

LaZnOPn (Pn=P and As) thin films were successfully grown on MgO (001) substrates with an epitaxial relationship of (001) LaZnOPn 11 (001) MgO and [110] LaZnOPn 11 [110] MgO. The electrical conductivity of undoped LaZnOP epitaxial film was so low, 3.1 x 10(-6) S/cm at room temperature, that reliable Seebeck and Hall measurement results were not obtained. On the other hand, the electrical conductivities of the Cu-doped LaZnOP and undoped LaZnOAs epitaxial films were 2.7 x 10(-2) and 2.0 x 10(-1) S/cm at room temperature, respectively. The Seebeck coefficients of both the epitaxial films were positive, indicating p-type semiconductors. The optical bandgaps of LaZnOP and LaZnOAs were estimated to be similar to 1.7 eV and similar to 1.5 eV, respectively. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2007.10.035

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記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

Structural, electronic, and magnetic properties of undoped and aliovalent-ion (Ca, F)-doped LaFePO, which undergo superconducting transitions at transition temperatures (T-c) 4-7 K [Y. Kamihara , J. Am. Chem. Soc. 128, 10012 (2006)], were investigated. T-c of the samples varied from 2.4 to 5.5 K in the undoped samples and was increased up to similar to 7 K by Ca and F doping. The T-c increases are correlated with a decrease in the lattice volume. LaFePO exhibits paramagnetism in the normal conducting state. Photoemission spectroscopy combined with first-principle band calculations clarified that Fe Fe 3d (d(z2)+(d(xz),d(yz))) orbitals hybridized with P 3p to form a Fermi surface. The band calculations also suggest that the 3d electron of the Fe in LaFePO is basically in the low-spin configuration, and that the spin moment of LaFePO is almost quenched, leading to the paramagnetism of the itinerant electrons.

DOI： 10.1103/PhysRevB.77.214515

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記述言語：英語   出版者・発行元：AMER PHYSICAL SOC  

The electronic and magnetic properties of cobalt-based layered oxypnictides, LaCoOX(X=P,As), are investigated. LaCoOP and LaCoOAs show metallic type conduction with room-temperature resistivities of similar to 2x10(-4) Omega cm, and the Fermi edge is observed by hard x-ray photoelectron spectroscopy. Ferromagnetic transitions occur at 43 K for LaCoOP and 66 K for LaCoOAs with spontaneous magnetic moments of 0.33 mu(B) and 0.39 mu(B) extrapolated to 0 K, respectively. Above the transition temperatures, the magnetic susceptibility exhibits a large temperature dependence. Provided that this temperature dependence follows the Curie-Weiss law, enhanced magnetic-moment values of similar to 2.9 mu(B) for LaCoOP and similar to 1.3 mu(B) for LaCoOAs are obtained. X-ray magnetic circular dichroism (XMCD) is observed at the Co L(2,3) edge, but not at the other edges. The calculated electronic structure shows a spin-polarized ground state with a magnetic moment of 0.52 mu(B), similar to 95% of which is localized on the Co ions. These results indicate that LaCoOX are itinerant ferromagnets and suggest that their magnetic properties are governed by spin fluctuation.

DOI： 10.1103/PhysRevB.77.224431

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

We investigated the electronic states in amorphous In-Ga-Zn-O films with high carrier concentrations by optical absorption and hard x-ray photoelectron spectroscopy (HX-PES). Films having different Hall mobilities were prepared and their annealing effects were examined. All HX-PES spectra showed Fermi edge structures and extra subgap densities of states (DOSs). Tail-like structures observed in the optical spectra originate from subgap DOSs (&gt;&gt; 10(20) cm(-3)) near valence band maximas (VBMs). Subgap DOSs near VBMs provide a reason why In-Ga-Zn-O thin film transistors show hard saturation in off states and are difficult to operate in an inversion p-channel mode. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2927306

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記述言語：英語  

DOI： 10.1063/1.2927306

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

Trap densities in amorphous-InGaZnO(4) (alpha-IGZO) are extracted directly from the capacitance-voltage characteristics of thin-film transistors at low frequencies. It is found that the trap densities are flat in the energy gap, and are 1.7x10(16) cm(-3) eV(-1) in the deep energy far from the conduction band edge (E(c)), but become larger near E(c). Moreover, postannealing reduces the trap density near E(c), which is associated with the reduction of the hysteresis in the current-voltage characteristics. The annealed alpha-IGZO does not have a Gaussian-type state and has fewer tail states than amorphous Si. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2904704

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

[Ca24Al28O64](4+)(O2-)(2-x)(e(-))(2x) (O &lt;= x &lt;= 2, C12A7:e(-)) crystal shows a metal-insulator transition at x similar to 1. Varied concentrations of electrons (N-e) are introduced in the subnanometer- sized crystallographic cages of [Ca24Al28O64](4+)(O2-)(2) (12CaO center dot 7Al(2)O(3), C12A7) in place of the O2- ions accommodated in the cages. The optical reflectance spectra of C12A7:e(-) crystals were analyzed using the Drude-Lorentz model to examine the electronic states and carrier transport mechanisms experimentally. The concentrations of localized electrons trapped in the cages were estimated from Lorentz-type optical responses around 0.4 and 2.8 eV, and those of delocalized electrons from a Drude-type response. C12A7:e(-) with N-e lower than 5 x 10(20) cm(-3) (x similar to 0.5) shows polaronic hopping conduction and its reflectance spectrum shows only the Lorentz-type responses. The Drude-type response starts to appear when N-e exceeds 5 x 10(20), and coexists with the Lorentz-type responses at Ne between 5 x 10(20) and 2 x 10(21) cm(-3) (x similar to 2), which indicates that the localized electrons coexist with the delocalized electrons even in the metallic samples. These results support previous theoretical studies proposing that a strong electron -l attice interaction deforms the soft cage structure of C12A7, and forming an insulating state at the low N-e limit, while the cage deformation is reduced at the high N-e limit, leading to the insulator-metal transition.

DOI： 10.1021/jp711631j

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記述言語：英語   出版者・発行元：A V S AMER INST PHYSICS  

Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical compositions of Zn: Sn= 1: 1 and 2: 1 as a function of oxygen partial pressure (Po-2) used for the film deposition and annealing temperature. Different from a previous report on sputter-deposited films [Chiang et al., Appl. Phys. Lett. 86, 013503 (2005)], the PLD-deposited films crystallized at a lower temperature &lt; 450 degrees C to give crystalline ZnO and SnO2 phases. The optical band gaps (Tauc gaps) were 2.80-2.85 eV and almost independent of oxygen PO2, which are smaller than those of the corresponding crystals (3.35-3.89 eV). Films deposited at low PO2 showed significant subgap absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases when carrier concentration exceeded threshold values and the threshold value depended on the film chemical composition. The films deposited at low Po-2 &lt; 2 Pa had low carrier concentrations. It is thought that the low Po-2 produced high-density oxygen deficiencies and generated electrons, but these electrons were trapped in localized states, which would be observed as the subgap absorptions. Similar effects were observed for 600 degrees C crystallized films and their resistivities were increased by formation of subgap states due to the reducing high-temperature condition. High carrier concentrations and large mobilities were obtained in an intermediate Po-2 region for the as-deposited films. (C) 2008 American Vacuum Society.

DOI： 10.1116/1.2839860

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

We report a model of the carrier transport and the subgap density of states in amorphous InGaZnO(4) (a-IGZO) for device simulation of a-IGZO thin-film transistors (TFTs) operated in both the depletion mode and the enhancement mode. A simple model using a constant mobility and two-step subgap density of states reproduced well the characteristics of the a-IGZO TFTs. a-IGZO exhibits low densities of tail states and deep gap states, leading to small subthreshold swings and high mobilities. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2857463

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE SA  

Thin film transistors (TFTs) using amorphous oxides of post-transition metals: indium, gallium, and zinc for the channel materials are fabricated with radio-frequency magnetron sputtering methods for the deposition of the channel and the gate insulator layers, at room temperature with no high-temperature post-deposition annealing process. The TFTs operate as n-channel field-effect transistors with various structures of top/ bottom gate and top/bottom source-and-drain contact including the inverse-stagger types, and with various materials for the gate insulators, the electrodes, and the substrates. The TFTs having smoother channel interfaces show the better performance at the saturation mobility beyond 10 cm(2) V-1 s(-1) and the on-to-off current ratio over 10(8) than the rough channel interfaces. The ring oscillator circuits operate with five-stage inverters of the top-gate TFTs or the inverse-stagger TFTs. Organic light-emission diode cells are driven by a simple circuit of the TFTs. It is also found by a combinatorial approach to the material exploration that the TFT characteristics can be controlled by the composition ratio of the metals in the channel layers. The amorphous oxide channel TFTs fabricated with sputtering deposition at low temperature could be a candidate for key devices of large-area flexible electronics. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2007.03.161

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

Crystal structures, optoelectronic properties, and electronic structures of layered oxychalcogenides BiCuOCh (Ch = S, Se, Te) have been compared to those of LaCuOCh, with an emphasis on the electronic configurations of Bi3+ (5d(10)6S(2)) and La3+ (5d(0)6s(0)). The BiCuOCh series were expected to exhibit better hole-transport properties than the LaCuOCh series because the pseudo-closed-shell 6S(2) electronic configuration of the Bi3+ cation was expected to form valence band maxima (VBM) by admixing with the p orbitals of the Ch anions. However, the two series of compounds exhibited similar electrical properties, suggesting that the contribution of the Bi 6s orbitals to the VBM is small in BiCuOCh. The crystal structures and optical properties showed distinct differences; for example, the band gaps of BiCuOCh were smaller than those of LaCuOCh. These findings can be understood on the basis of the electronic structures obtained by photoelectron spectroscopy and density functional theory calculations. The Bi 6s orbitals form stronger and deeper chemical bonds with the O 2p orbitals than with Ch p orbitals and are located similar to 2 eV below the VBM, which is mainly formed from the Cu 3d and Ch p orbitals. Thus, the Bi 6s(2) configuration contributes little to the VBM, and BiCuOCh and LaCuOCh have similar hole-transport properties. Also, the smaller band gaps of BiCuOCh result from the deepening of the conduction-band-minima levels, which are composed of unoccupied Bi 6p orbitals.

DOI： 10.1021/cm702303r

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DOI： 10.1002/pssa.200778850

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記述言語：日本語   出版者・発行元：公益社団法人 日本化学会  

私たちの周りには,窓ガラス,コンクリート,茶碗など,酸化物があふれている。多くの人がこれらから受ける酸化物の印象は,「透明(白い)」「硬い」「電気を流さない」ではないだろうか。酸化物はコンピュータなどの電子機器にも使われているが,特に最後の「電気的に面白い特性をもたない」という性質のため,機器の構造を支えたり電気的な絶縁をしたりするための脇役でしかなかった。酸化物に電気を流せないのは,それらがイオン性物質であるからでも透明であるからでもなく,電子を余計に加えたり,抜いたりすることがうまくいかなかったからなのである。材料の構成元素をうまく選び,作り方や微量不純物の加え方を工夫することで,酸化物でも高い電気伝導性を得ることができる。このような材料は「透明導電性酸化物」と呼ばれ,平面テレビや太陽電池に不可欠な材料であるだけでなく,次世代有機ELテレビの電子素子としても開発が進められている。

DOI： 10.20665/kakyoshi.56.12_598

CiNii Books

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DOI： 10.1016/j.jnoncrysol.2007.10.071

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記述言語：英語   出版者・発行元：WILEY-V C H VERLAG GMBH  

Defect states in a representative amorphous oxide semiconductor, a-InGaZnO4, were studied by optical analyses and first-principle calculations. The optical analyses suggested that the as-deposited a-IGZO film have weak subgap absorptions around 0.6 and 2 eV. Local density approximation calculations showed that an oxygen defect works as an electron trap as well as a shallow donor depending on its local structure. It suggests that a large vacancy space remained in an oxygen deficient structure forms a deep levels in the band gap and traps electrons, while if such a large space is annihilated e.g. by a film growth process and post thermal annealing, oxygen deficiency may form a shallow donor level. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200779300

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DOI： 10.1016/j.jnoncrysol.2007.09.090

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記述言語：日本語   出版者・発行元：シーエムシー出版  

CiNii Books

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記述言語：日本語   出版者・発行元：日本表面科学会  

DOI： 10.1380/jsssj.29.2

CiNii Books

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記述言語：英語  

Defect states in a representative amorphous oxide semiconductor, a-InGaZnO4, were studied by optical analyses and first-principle calculations. The optical analyses suggested that the as-deposited a-IGZO film have weak subgap absorptions around 0.6 and 2 eV. Local density approximation calculations showed that an oxygen defect works as an electron trap as well as a shallow donor depending on its local structure. It suggests that a large vacancy space remained in an oxygen deficient structure forms a deep levels in the band gap and traps electrons, while if such a large space is annihilated e.g. by a film growth process and post thermal annealing, oxygen deficiency may form a shallow donor level. © 2008 Wiley-VCH Verlag GmbH &amp
Co. KGaA.

DOI： 10.1002/pssc.200779300

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DOI： 10.1557/mrs2008.226

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DOI： 10.1016/j.jnoncrysol.2007.09.090

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DOI： 10.1021/jp711631j

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DOI： 10.1063/1.3020714

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DOI： 10.1103/PhysRevB.77.224431

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DOI： 10.1103/PhysRevB.77.214515

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DOI： 10.1149/1.2903866

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

A layered oxyphosphide, LaNiOP, was synthesized by solid-state reactions. This crystal was confirmed to have a layered structure composed of an alternating stack of (La3+O2-)(+) and (Ni2+P3-)(-). We found that the resulting LaNiOP shows a superconducting transition at similar to 3 K. This material exhibited metallic conduction and Pauli paramagnetism in the temperature range of 4-300 K. The resistivity sharply dropped to Zero, and the magnetic susceptibility became negative at &lt;4 K, indicating that a superconducting transition occurs. The volume fraction of the superconducting phase estimated from the diamagnetic susceptibility reached similar to 40 vol % at 1.8 K, substantiating that LaNiOP is a bulk superconductor.

DOI： 10.1021/ic701200e

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

The high density hole doping (1.7x10(21) cm(-3)) for a wide gap (E-g=similar to 2.8 eV) p-type semiconductor was achieved on 40 nm thick Mg-doped LaCuOSe epitaxial films. These films exhibited distinct free carrier absorption, and the effective mass and momentum relaxation time were analyzed. Its small hole mobility [similar to 3.5 cm(2)/(V s)] compared to the electron mobilities of wide gap n-type semiconductors is attributed to a heavy effective mass of 1.6 +/- 0.2m(e). Regardless of the heavy hole doping, a band filling effect was not observed. These results are discussed with a rigid band model and an acceptor band model. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2753546

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記述言語：英語   出版者・発行元：AMER CHEMICAL SOC  

12CaO center dot 7Al(2)O(3) electride (C12A7:e(-)) is a promising material for the cathode of organic light-emitting diodes (OLEDs), because it has a low work function (phi(WF) = 2.4 eV), comparable to metal potassium, and good chemical/thermal stability in an ambient atmosphere. This study examines interfacial electronic structures between C12A7:e(-) and tris-8-hydroxyquinoline aluminum (Alq(3)) by ultraviolet photoelectron spectroscopy, finding that a low electron-injection barrier of 0.6 eV, which is approximately half of the value for the Al/LiF/Alq(3) interface with the lowest injection barrier, is achieved when the interface is formed on the C12A7:e(-) film surface obtained by using vacuum annealing and subsequent He plasma treatment. This treatment yields little change in the surface chemical composition and retains a low phi(WF) value (3.1 eV) of C12A7:e(-). These results suggest that C12A7:e(-) has high potential as an efficient electron-injection electrode for OLEDs.

DOI： 10.1021/jp072635r

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記述言語：英語  

We report a metallic state in a nanostructured porous crystal 12CaO-7Al2O3 by incorporating electrons in the inherent subnanometer-sized cages, in which a three-dimensionally closely packed cage structure acts as an electronic conduction path. High-density electron doping (∼2 x 1021 cm-3), which was achieved by a thermal treatment in Ti metal vapor at ∼1100 °C, induces homogenization of the cage geometry to a symmetric state, resulting in an insulator-metal transition with a sharp enhancement of the electron drift mobility from ∼0.1 to 4 cm2 V-1 s-1. The results provide an approach for the realization of electroactive functions in materials composed only of environmentally benign elements by utilizing the appropriate nanostructures. © 2007 American Chemical Society.

DOI： 10.1021/nl062717b

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