Suppression of Screw Dislocation-Induced Hillocks in MOCVD-Grown α-Ga2O3 on m-Plane Sapphire by Introducing a High-Temperature Buffer

α-Gallium oxide (Ga₂O₃) has great potential in the applications of high-power, high-frequency, and energy-saving electronic devices. In this study, we successfully grew pure-phase α-Ga₂O₃ films on m-plane sapphire substrates by using metal organic chemical vapor deposition (MOCVD) and systematically investigated the impact of various growth parameters on the resulting film characteristics. The crystallization quality of the films improved by adjusting the VI/III ratio, ultimately yielding a symmetric rocking curve full width at half-maximum (fwhm) of 0.39° for the (300) diffraction. The surface morphology of α-Ga₂O₃ films exhibited a layer-by-layer growth mode, characterized by a remarkably flat surface (RSM = 0.365 nm) in the early growth stage. Nevertheless, as the film thickness increased, the appearance of hillock defects composed of β-Ga₂O₃ detrimentally impacted the surface quality. To mitigate this issue, a high-temperature buffer layer was introduced to inhibit the formation of hillocks. This approach resulted in α-Ga₂O₃ films on m-plane sapphire with substantial thickness and exceptional surface quality, establishing a robust foundation for the future fabrication of heterojunction devices.