Carrier-generation mechanism in Zn-doped In₂O₃ transparent conductors

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 (Zn_i) and substitutional Zn(Zn_In), Zn_In is found to be energetically more favorable. While Zn_In acts as an acceptor, potentially compensating for n-type doping, it readily forms a defect complex, Zn_In-V_O, by combining with oxygen vacancies (V_Os), 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 Zn_In-V_O 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.