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Title: Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations

Abstract

Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of {approx}10 cm{sup 2} V{sup -1} s{sup -1} [K. Nomura et al., Nature 488, 432 (2004)]. The local coordination structure in an IAOS, In-Ga-Zn-O (a-IGZO), was examined using extended x-ray absorption fine structure analysis combined with ab initio calculations. The short-range ordering and coordination structures in a-IGZO are similar to those in the corresponding crystalline phase, InGaZnO{sub 4}, and edge-sharing structures consisting of In-O polyhedra remain in the amorphous structure. The In{sup 3+} 5s orbitals form an extended state with a band effective mass of {approx}0.2m{sub e} at the conduction band bottom.

Authors:
; ;  [1];  [1];  [2];  [3];  [1];  [2];  [2]
  1. ERATO-SORST, JST, in Frontier Collaborative Research Center, Mail Box S2-13, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
  2. (Japan)
  3. SPring-8, Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Mikazuki-cho, Hyogo 679-5198 (Japan)
Publication Date:
OSTI Identifier:
20976656
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevB.75.035212; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; ABSORPTION SPECTROSCOPY; EFFECTIVE MASS; ELECTRON MOBILITY; ELECTRONIC STRUCTURE; FINE STRUCTURE; GALLIUM COMPOUNDS; INDIUM COMPOUNDS; INDIUM IONS; OXIDES; SEMICONDUCTOR MATERIALS; THIN FILMS; TRANSISTORS; X RADIATION; X-RAY SPECTROSCOPY

Citation Formats

Nomura, Kenji, Ohta, Hiromichi, Hirano, Masahiro, Kamiya, Toshio, Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Uruga, Tomoya, Hosono, Hideo, Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, and Frontier Collaborative Research Center, Mail Box S2-13, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama 226-8503. Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.035212.
Nomura, Kenji, Ohta, Hiromichi, Hirano, Masahiro, Kamiya, Toshio, Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Uruga, Tomoya, Hosono, Hideo, Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, & Frontier Collaborative Research Center, Mail Box S2-13, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama 226-8503. Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations. United States. doi:10.1103/PHYSREVB.75.035212.
Nomura, Kenji, Ohta, Hiromichi, Hirano, Masahiro, Kamiya, Toshio, Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Uruga, Tomoya, Hosono, Hideo, Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, and Frontier Collaborative Research Center, Mail Box S2-13, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama 226-8503. Mon . "Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations". United States. doi:10.1103/PHYSREVB.75.035212.
@article{osti_20976656,
title = {Local coordination structure and electronic structure of the large electron mobility amorphous oxide semiconductor In-Ga-Zn-O: Experiment and ab initio calculations},
author = {Nomura, Kenji and Ohta, Hiromichi and Hirano, Masahiro and Kamiya, Toshio and Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 and Uruga, Tomoya and Hosono, Hideo and Materials and Structures Laboratory, Mail Box R3-1, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 and Frontier Collaborative Research Center, Mail Box S2-13, Tokyo Institute of Technology, 4259, Nagatsuta, Midori-ku, Yokohama 226-8503},
abstractNote = {Ionic amorphous oxide semiconductors (IAOSs) are new materials for flexible thin film transistors that exhibit field-effect mobilities of {approx}10 cm{sup 2} V{sup -1} s{sup -1} [K. Nomura et al., Nature 488, 432 (2004)]. The local coordination structure in an IAOS, In-Ga-Zn-O (a-IGZO), was examined using extended x-ray absorption fine structure analysis combined with ab initio calculations. The short-range ordering and coordination structures in a-IGZO are similar to those in the corresponding crystalline phase, InGaZnO{sub 4}, and edge-sharing structures consisting of In-O polyhedra remain in the amorphous structure. The In{sup 3+} 5s orbitals form an extended state with a band effective mass of {approx}0.2m{sub e} at the conduction band bottom.},
doi = {10.1103/PHYSREVB.75.035212},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 3,
volume = 75,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • The origin of the high nonlinear optical response in tellurite glasses is tentatively elucidated from a detailed structural investigation of typical glasses existing in the TeO{sub 2}-Al{sub 2}O{sub 3} and TeO{sub 2}-Nb{sub 2}O{sub 5} systems joined to a study of their electronic properties through ab initio calculations. As the proportions of Al{sub 2}O{sub 3} or Nb{sub 2}O{sub 5} increase, the TeO{sub 4} trigonal bipyramids are progressively transformed into a TeO{sub 3+1} asymetric polyhedron, the geometry of which is actually very close to the TeO{sub 3} trigonal pyramids already found in some crystal structures, e.g., in ZnTeO{sub 3}. Ab initio calculationsmore » have been performed on TeO{sub 4} and TeO{sub 3} clusters. The highest occupied molecular orbital is of antibonding type and combines 5s AO of tellurium and 2p AO of oxygens. The energy difference between these orbitals and the next vacant molecular orbital is lower for the TeO{sub 4} entity than for the TeO{sub 3} cluster. This result is consistent with a higher polarizability of the TeO{sub 4} entity and accordingly with the higher nonlinear index coefficient n{sub 2} of the richest tellurium glasses.« less
  • Electronic structure of oxygen vacancies in Ta{sub 2}O{sub 5} have been studied theoretically by first-principles calculations and experimentally by x-ray photoelectron spectroscopy. Calculations of {delta}-Ta{sub 2}O{sub 5} were performed using density functional theory within gradient-corrected approximation with the +U approach. Results indicate that the oxygen vacancy causes a defect level in the energy gap at 1.2 eV above the top of the valence band. To produce oxygen vacancies, amorphous films of Ta{sub 2}O{sub 5} were bombarded with Ar{sup +} ions. XPS results indicate that the Ar-ion bombardment leads to the generation of the oxygen vacancies in Ta{sub 2}O{sub 5} thatmore » characterize the peak at 2 eV above the valence band. The calculated spectrum of crystalline {delta}-Ta{sub 2}O{sub 5} demonstrates qualitative correspondence with the XPS spectrum of the amorphous Ta{sub 2}O{sub 5} film after Ar-ion bombardment.« less
  • Amorphous In-Ga-Zn-O (a-IGZO) is expected as a backplane transistor material to drive next-generation flat-panel and flexible displays. It has been elucidated that thermal annealing even at low temperatures <200 deg. C reduces deep subgap defects and those at {>=}300 deg. C further improve device characteristics, stability, and uniformity. These temperatures are much lower than the reported crystallization temperature (T{sub X}{approx} 600 deg. C). In this work, we investigate effects of thermal annealing on the structural and optical properties of a-IGZO thin films. We performed classical molecular dynamics simulation (CMD) and optical interference analyses including spectroscopic ellipsometry (SE). CMD reproduced themore » x-ray diffraction pattern of a-IGZO and exhibited a glass transition. Experimentally, it was found that T{sub X} depends largely on deposition methods and conditions, probably due to different chemical compositions. Sputter-deposited a-IGZO films exhibited onset T{sub X}{approx} 600 deg. C and crystalline volume fraction X{sub C} increased linearly from 600 deg. C. 1.2% of film densification occurred even at 600 deg. C due to crystallization. High-temperature in situ SE measurements did not detect a symptom of a glass transition temperature (T{sub g}) presumably because the T{sub X} is close to T{sub g} similar to the case of amorphous metals.« less
  • The electronic structure of an oxygen vacancy in {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3} is calculated. The calculation predicts an absorption peak at an energy of 6.4 and 6.3 eV in {alpha}-Al{sub 2}O{sub 3} and {gamma}-Al{sub 2}O{sub 3}, respectively. The luminescence and luminescence excitation spectra of amorphous Al{sub 2}O{sub 3} are measured using synchrotron radiation. The presence of a luminescence band at 2.9 eV and a peak at 6.2 eV in the luminescence excitation spectrum indicates the presence of oxygen vacancies in amorphous Al{sub 2}O{sub 3}.