  Ga2O3 is being actively explored for high-power and high-temperature
electronics, deep-ultraviolet optoelectronics, and other applications.
Efficient n-type doping of Ga2O3 has been achieved, but p-type doping faces
fundamental obstacles due to compensation, deep acceptor levels, and the
polaron transport mechanism of free holes. However, aside from achieving p-type
conductivity, plenty of opportunity exists to engineer the position of the
Fermi level for improved design of Ga2O3 based devices. We use first-principles
defect theory and defect equilibrium calculations to simulate a 3-step
growth-annealing-quench synthesis protocol for hydrogen assisted Mg doping in
beta-Ga2O3, taking into account the gas phase equilibrium between H2, O2 and
H2O, which determines the H chemical potential. We predict Ga2O3 doping-type
conversion to a net p-type regime after growth under reducing conditions in the
presence of H2 followed by O-rich annealing, which is a similar process to the
Mg acceptor activation by H removal in GaN. For equilibrium annealing there is
an optimal temperature that maximizes the Ga2O3 net acceptor density for a
given Mg doping level, which is further increased in the non-equilibrium
annealing scenario without re-equilibration. After quenching to operating
temperature, the Ga2O3 Fermi level drops below mid-gap down to about +1.5 eV
above the valence band maximum, creating a significant number of uncompensated
neutral MgGa0 acceptors. The Fermi level reduction down to +1.5 eV and
suppression of free electron density in this doping type converted (NA > ND)
Ga2O3 material is of significance and impact for the design of Ga2O3 power
electronics devices.
