Gallium Oxide Thin Films Grown by Mist Chemical Vapor Deposition on Quartz Substrates Hydrophilized by UV Irradiation

Abstract

Gallium oxide (Ga₂O₃) is known to be an ultrawide-gap semiconductor material and is expected to have applications in power semiconductor devices and optical devices for deep ultraviolet (UV) light. In this study, as a continuation of our paper published in this journal in FY2024, we report experimental results of Ga₂O₃ thin films grown by mist chemical vapor deposition (CVD) method on quartz substrates whose surfaces are made hydrophilic by UV irradiation. For the equipment used in this study, the optimum UV irradiation time for the quartz substrate was 60 minutes. Amorphous Ga₂O₃ thin films were grown on the quartz substrates at substrate temperatures of 450°C and 500°C, while a mixture of β-Ga₂O₃ and amorphous Ga₂O₃ thin film was obtained when grown at 550°C. The surface roughness of the amorphous Ga₂O₃ thin films were low, but the surface roughness deteriorated when β-Ga₂O₃ was intermixed. The optical absorption properties showed high transmittance of more than 85% for all samples in visible region. The optical absorption edges were like that of β-Ga₂O₃ at growth temperatures of 450°C and 500°C, but became shorter at 550°C. It was found that amorphous Ga₂O₃ was deposited without hydrophilization, but the surface roughness deteriorated compared to that with hydrophilization. In the previous report, hydrophilization was performed with hydrofluoric acid, but the method using UV irradiation was found to provide better crystal growth with less variation in results, especially at a growth temperature of 500°C.