Temperature Dependence of Ultrathin Mixed-Phase GaO Films Grown on the α-AlO Substrate via Mist-CVD.

Alpha (α)- and beta (β)-phase gallium oxide (GaO), 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 GaO thin films on the α-AlO 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 GaO ultrathin film on the α-AlO 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 GaO film possesses a mixed α- and β-phase with an average value of dislocation density of 10 cm for all growth temperatures, indicating a high lattice mismatch between the film and the substrate. At 600 °C, the ultrathin and smooth GaO 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 GaO ultrathin film can have great potential in developing future high-power electronic devices.