Conductivity Limits in CuAlO2 from Screened-Hybrid Density Functional Theory

CuAlO2 is a prototypical delafossite p-type transparent conducting oxide (TCO). Despite this many fundamental questions about its band structure and conductivity remain unanwered. We utilize the screened hybrid exchange functional (HSE06) to investigate defects in CuAlO2 and find that copper vacancies and copper on aluminium antisites will dominate under Cu-poor/Al-poor conditions. Our calculated transitions levels are deep in the band gap consistent with experimental findings, and we identify the likely defect levels that are often mistaken as indirect band gaps. Finally, we critically discuss delafossite oxides as TCO materials.