The unique response of amorphous ionic oxides to changes in oxygen stoichiometry is investigated using computationally intensive ab initio molecular dynamics simulations, comprehensive structural analysis, and hybrid density-functional calculations for the oxygen defect formation energy and electronic properties of amorphous In2O3-x with x = 0-0.185. In marked contrast to nonstoichiometric crystalline nanocomposites with clusters of metallic inclusions inside an insulating matrix, the lack of oxygen in amorphous indium oxide is distributed between a large fraction of undercoordinated In atoms, leading to an extended shallow state for x < 0.037, a variety of weakly and strongly localized states for 0.074 < x < 0.148, and a percolation-like network of single-atom chains of metallic In-In bonds for x > 0.185. The calculated carrier concentration increases from 3.3 x 1020cm-3 at x = 0.037 to 6.6 x 1020 cm-3 at x=0.074 and decreases only slightly at lower oxygen content. At the same time, the density of deep defects located between 1 and 2.5 eV below the Fermi level increases from 0.4 x 1021 cm-3 at x = 0.074 to 2.2 x 1021 cm-3 at x = 0.185. The wide range of localized gap states associated with various spatial distributions and individual structural characteristics of undercoordinated In is passivated by hydrogen that helps enhance electron velocity from 7.6 x 104 to 9.7 x 104 m/s and restore optical transparency within the visible range; H doping is also expected to improve the material's stability under thermal and bias stress.




The authors acknowledge the support from the National Science Foundation (NSF) DMREF Grants No. DMR-1729779 and No. DMR-1842467. The computational resources were provided by Missouri S&T and NSF-MRI Grant No. OAC-1919789.

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01 Feb 2022

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