Prospects for n-type doping of (AlxGa1-x)2O3 alloys

We systematically explore the properties of group-IV (C, Si, Ge, and Sn) and transition metal (Hf, Zr, and Ta) dopants substituting on the cation site in (AlxGa1-x)(2)O-3 (AlGO) alloys using first-principles calculations with a hybrid functional. In Ga2O3, each of these dopants acts as a shallow donor. In Al2O3, they are deep defects characterized by the formation of either DX centers or positive-U (+/0) levels. Combining our calculations of dopant charge-state transition levels with information of the AlGO alloy band structure, we estimate the critical Al composition at which each dopant transitions from being a shallow to a deep donor. We identify Si to be the most efficient dopant to achieve n-type conductivity in high Al-content AlGO alloys, acting as a shallow donor over the entire predicted stability range for AlGO solid solution alloys.