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

Alpha (α)- and beta (β)-phase gallium oxide (Ga 2 O 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 2 O 3 thin films on the α-Al 2 O 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 2 O 3 ultrathin film on the α-Al 2 O 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 2 O 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 2 O 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 2 O 3 ultrathin film can have great potential in developing future high-power electronic devices.