Electronic structure of oxygen deficient amorphous oxide semiconductor a‐InGaZnO4–x: Optical analyses and first‐principle calculations

Abstract Defect states in a representative amorphous oxide semiconductor, a‐InGaZnO 4 , were studied by optical analyses and first‐principle calculations. The optical analyses suggested that the as‐deposited a‐IGZO film have weak subgap absorptions around 0.6 and 2 eV. Local density approximation calculations showed that an oxygen defect works as an electron trap as well as a shallow donor depending on its local structure. It suggests that a large vacancy space remained in an oxygen deficient structure forms a deep levels in the band gap and traps electrons, while if such a large space is annihilated e.g. by a film growth process and post thermal annealing, oxygen deficiency may form a shallow donor level. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)