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

2014; American Institute of Physics; Volume: 104; Issue: 23 Linguagem: Inglês

10.1063/1.4883257

1520-8842

Shawn Sallis, Keith T. Butler, Nicholas F. Quackenbush, D. S. Williams, Maxwell M. Junda, D. A. Fischer, J. C. Woicik, Nikolas J. Podraza, B. E. White, Aron Walsh, Louis F. J. Piper,

Silicon Nanostructures and Photoluminescence

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.