Spontaneous Donor Defects and Voltage-Assisted Hole Doping in Beta-Gallium Oxides under Multiple Epitaxy Conditions

Beta-phase gallium oxide (β-Ga 2 O 3 ) is prone to the spontaneous formation of donor defects but poses a formidable challenge in achieving high-quality p-type doping, mainly due to its exceptionally low valence band maximum (VBM). In this study, we utilize first-principles computations to investigate the origin of spontaneous donor defects in β-Ga 2 O 3 grown by three typical techniques: molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), and halide vapor phase epitaxy (HVPE). Our findings elucidate that the primary donor defects vary with the growth techniques, specifically Ga i 3+ for MBE, H i + and C Ga + for MOCVD, and (2 V Ga +Ga i +2 V O ) + and Cl O + for HVPE under unintentionally doped conditions. Employing a theoretically proposed voltage-assisted doping method, we computationally demonstrate that the dominant spontaneous donors can be significantly reduced accompanied by a noticeable increase in acceptors, leading to stepwise reductions of Fermi levels to 0.52, 0.88, and 2.10 eV above VBM for the MOCVD, HVPE, and MBE methods and hole concentrations of 8.5 × 10 17, 8.7 × 10 11, and 2.7 × 10 –9 cm –3, respectively, at room temperature without the use of external dopants. By introducing Mg doping, we further reduce the Fermi levels for both the MBE and HVPE experiments.