Subgap States near the Conduction-Band Edge Due to Undercoordinated Cations in Amorphous In-Ga-Zn-O and Zn-Sn-O Semiconductors

Abstract

Amorphous oxide semiconductors are promising channel materials for transparent, flexible thin-film transistors, but actual devices suffer from instability in threshold voltage, due to structural defects. First-principles calculations reveal that undercoordinated cations in nonstoichiometric samples lead to localized subgap states that are the root of the instability. These results establish a physical understanding of the precise origin of these states, and offer guidance to control such defects for successful applications.