RF magnetron sputtering of β-Ga₂O₃ thin films: a critical process-map review of growth regimes, parameter coupling, and conditional process windows

Abstract β-Ga₂O₃ has attracted significant attention as an ultra-wide-bandgap semiconductor for high-power electronics, solar-blind photodetectors, and sensors operating in extreme environments owing to its wide bandgap, high critical electric field, and the commercial availability of melt-grown substrates. Radio frequency (RF) magnetron sputtering is a scalable and economical thin-film deposition technique; however, correlations between sputtering conditions and β-Ga₂O₃ film properties remain less systematically established than those for mature epitaxial methods. This review critically examines RF magnetron-sputtered β-Ga₂O₃ thin films with emphasis on substrate selection, substrate temperature, RF power, oxygen-to-argon ratio, sputtering pressure, and post-deposition annealing. The reviewed literature indicates that high-quality films are most consistently obtained on c-plane sapphire, with conventional in situ growth temperatures of approximately 650-800 °C, moderate RF power near 100-120 W, nominal, system-dependent O₂/Ar ratios commonly around 5-10% and in some systems extending toward ~15%, intermediate sputtering pressures near 6-10 mTorr, and post-deposition annealing at 800-1000 °C when low-temperature growth is used. These ranges should not be interpreted as universal recipes; rather, they define conditional process windows that depend on target geometry, plasma conditions, oxygen activity, pressure-dependent scattering, film thickness, and thermal history. By organizing recent studies into coupled growth regimes, this review provides a process-map framework for improving reproducibility and guiding application-specific β-Ga₂O₃ thin-film deposition by RF magnetron sputtering.