The Nature of the Oxygen Vacancy in Amorphous Oxide Semiconductors: Shallow Versus Deep

Using first-principles calculation, we investigate the nature of oxygen vacancy (V-O), namely shallow versus deep, in the amorphous oxide semiconductor InGaZnO4 (a-IGZO), which has not been fully clarified despite its technological importance. Oxygen-deficient amorphous models are generated through the hybrid functional molecular dynamics (MD) simulations that allow for finding stable V-O configurations while minimizing computational approximations. From eight independent models, we consistently find that V-O serves as the shallow donor, increasing the Fermi level above the conduction band minimum. For comparison purpose, we also generate deep V-O models by charging the system during MD simulations. It is found that deep V-O is higher in the formation energy than shallow V-O, confirming that shallow V-O is the preferred type of oxygen vacancies in a-IGZO.