Oxygen effect on the performance of β-Ga2O3 enhancement mode MOSFETs heteroepitaxially grown on a sapphire

β-Ga₂O₃ is regarded as a promising candidate for next-generation high-power devices; however, the impact of material quality on device performance is significant and not yet well understood. In this study, β-Ga₂O₃ heteroepilayers were grown on c-plane sapphire using metalorganic chemical vapor deposition (MOCVD) at three different O₂ flow rates. Enhancement-mode β-Ga₂O₃ metal-oxide-semiconductor field-effect transistors (MOSFETs) were then fabricated with a gate-recessed process, incorporating a 5 µm gate field plate structure. Higher O₂ flow rates resulted in increased breakdown voltage. X-ray photoelectron spectroscopy analysis suggests that this improvement is due to reduced oxygen vacancies and minimized Al diffusion from the substrate. First-principle simulations further confirmed this phenomenon.