The effects of high temperature thermal treatments on β-Ga₂O₃ films grown on c-sapphire by low-pressure CVD

As a simple and effective method for improving the crystalline quality of epitaxial Ga₂O₃ film, post-thermal treatment has been identified as a competitive process involving crystal reconstruction accompanied by defect formation. In this study, β-Ga₂O₃ films grown on a c-sapphire substrate using low-pressure chemical vapor deposition were subjected to thermal treatment at 1000 °C in air for various duration to investigate the effects of treatment time on the films. The full width at half maximum (FWHM) of x-ray rocking curves initially decreased from 1.62° to 0.98° with increasing treatment time up to 5 h, indicating improved crystallinity. This improvement is likely a result of the reduced angle between Ga₂O₃ grains and the reconstructed Ga₂O₃ lattice, oriented towards the (−201) plane due to the thermal treatment, as observed in the transmission electron microscope and electron back-scattering diffraction results. However, under 7 h of treatment, the crystallinity of Ga₂O₃ degraded, as evidenced by an increased FWHM, as well as by x-ray photoelectron spectroscopy, photoluminescence, and time-of-flight secondary ion mass spectrometry results. This degradation can be attributed to the presence of massive oxygen vacancies and the substitutional incorporation of nitrogen into oxygen sites (N_O), resulting in defects.