via three-step processing*

Ga₂O₃ is being actively explored for power electronics, and other applications due to its ultra-wide bandgap and low projected fabrication cost of high-quality crystals. N-type doping of Ga₂O₃ can be achieved and tuned, but p-type doping faces fundamental obstacles. Successful engineering of Ga₂O₃ based devices requires critical control of doping density, Fermi level position, providing opportunities for predictive process simulation. We use first-principles defect equilibrium calculations to simulate a 3-step growth-annealing-quench protocol for hydrogen assisted Mg doping in Ga₂O₃, taking into account the hydrogen-oxygen-water gas phase equilibrium. We predict type conversion to a net p-type regime following O-rich annealing after growth under reducing conditions in the presence of H₂. We show that there is an optimal temperature that maximizes the net acceptor density during the equilibrium annealing step for a given Mg doping level. Quenching of non-equilibrium annealed samples then results in a Fermi level E_F below mid-gap down to about E_V +1.5 eV, creating a significant number of uncompensated neutral Mg_Ga⁰ acceptors. This type converted Ga₂O₃ can create significant built-in field in a p-n junction with an adjoining n-type material and could enable vertical MOSFETs.