Theoretical confirmation of the polaron model for the Mg acceptor in β-Ga2O3

β-Ga2O3 has recently been considered for power electronics applications but p-type doping is an issue, especially since small hole polarons were predicted and observed in this material. Recently, by using a gap-optimized, Koopmans-compliant hybrid functional, we were able to reproduce the observed charge transition levels of defects, including the hole polaron in the intrinsic material. In this study, the same hybrid functional is used to confirm the assignment of the electron paramagnetic resonance (EPR) spectrum observed in Mg-doped β-Ga2O3 samples. The Mg impurity introduces a deep acceptor level in β-Ga2O3 corresponding to a small polaron, localized at an oxygen site adjacent to the substitutional Mg. The so-called O1 site is energetically favored and the superhyperfine interactions with the neighboring tetrahedrally coordinated Ga atom are 1.9 times stronger than with the neighboring octahedrally coordinated Ga. The calculated hyperfine tensor agrees well with the EPR measurement. These results confirm that Mg cannot act as a shallow acceptor in β-Ga2O3.