Temperature Dependence of Ultrathin Mixed-Phase Ga ₂O ₃ Films Grown on the α-Al ₂O ₃ Substrate via Mist-CVD

Abstract

Alpha (α)- and beta (β)-phase gallium oxide (Ga ₂O ₃), emerging as ultrawide-band gap semiconductors, have been paid a great deal of attention in optoelectronics and high-performance power semiconductor devices owing to their ultrawide band gap ranging from 4.4 to 5.3 eV. The hot-wall mist chemical vapor deposition (mist-CVD) method has been shown to be effective for the growth of pure α- and β-phase Ga ₂O ₃ thin films on the α-Al ₂O ₃ substrate. However, challenges to preserve their intrinsic properties at a critical growth temperature for robust applications still remain a concern. Here, we report a convenient route to grow a mixed α- and β-phase Ga ₂O ₃ ultrathin film on the α-Al ₂O ₃ substrate via mist-CVD using a mixture of the gallium precursor and oxygen gas at growth temperatures, ranging from 470 to 700 °C. The influence of growth temperature on the film characteristics was systematically investigated. The results revealed that the as-grown Ga ₂O ₃ film possesses a mixed α- and β-phase with an average value of dislocation density of 10 ¹⁰ cm ^–2 for all growth temperatures, indicating a high lattice mismatch between the film and the substrate. At 600 °C, the ultrathin and smooth Ga ₂O ₃ film exhibited a good surface roughness of 1.84 nm and an excellent optical band gap of 5.2 eV. The results here suggest that the mixed α- and β-phase Ga ₂O ₃ ultrathin film can have great potential in developing future high-power electronic devices.