Carrier-generation mechanism in Zn-doped In2O3 transparent conductors

Abstract

Zn-doped In2O3 (IZO) has been extensively studied as a transparent conducting oxide (TCO) due to its favorable optical and electrical characteristics. In this work, to uncover the origin of degenerate n-type doping in IZO, we investigated point defects using density functional theory (DFT) calculations. Among the two possible configurations of Zn dopants, namely interstitial (Zni) and substitutional Zn(ZnIn), ZnIn is found to be energetically more favorable. While ZnIn acts as an acceptor, potentially compensating for n-type doping, it readily forms a defect complex, ZnIn-VO, by combining with oxygen vacancies (VOs), the dominant intrinsic defects in In2O3. This defect complex exhibits a substantial binding energy of approximately 1 eV and functions as a shallow donor. By evaluating carrier concentrations that can occur in IZO films, we demonstrate that the formation of ZnIn-VO is critical to maintaining or even enhancing significant n-type conductivities of IZO. By elucidating the doping behavior of IZO, this work provides critical insights to optimize its properties, thereby helping the advancement of optoelectronic and energy devices where IZO serves as a vital TCO.