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Title: Origin of deep subgap states in amorphous indium gallium zinc oxide: Chemically disordered coordination of oxygen

The origin of the deep subgap states in amorphous indium gallium zinc oxide (a-IGZO), whether intrinsic to the amorphous structure or not, has serious implications for the development of p-type transparent amorphous oxide semiconductors. We report that the deep subgap feature in a-IGZO originates from local variations in the oxygen coordination and not from oxygen vacancies. This is shown by the positive correlation between oxygen composition and subgap intensity as observed with X-ray photoelectron spectroscopy. We also demonstrate that the subgap feature is not intrinsic to the amorphous phase because the deep subgap feature can be removed by low-temperature annealing in a reducing environment. Atomistic calculations of a-IGZO reveal that the subgap state originates from certain oxygen environments associated with the disorder. Specifically, the subgap states originate from oxygen environments with a lower coordination number and/or a larger metal-oxygen separation.
Authors:
;  [1] ; ;  [2] ;  [3] ; ;  [4] ; ;  [5] ; ;  [3] ;  [6]
  1. Materials Science and Engineering, Binghamton University, Binghamton, New York 13902 (United States)
  2. Center for Sustainable Technologies and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY (United Kingdom)
  3. Department of Physics, Applied Physics, and Astronomy, Binghamton University, Binghamton, New York 13902 (United States)
  4. Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606 (United States)
  5. Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)
  6. (United States)
Publication Date:
OSTI Identifier:
22300009
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 104; Journal Issue: 23; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AMORPHOUS STATE; ANNEALING; CORRELATIONS; GALLIUM COMPOUNDS; INDIUM COMPOUNDS; OXYGEN; SEMICONDUCTOR MATERIALS; VACANCIES; X-RAY PHOTOELECTRON SPECTROSCOPY; ZINC OXIDES