β-Ga₂O₃ is an ultra-wide bandgap semiconductor promising for high-power electronic applications; however, heteroepitaxial growth on sapphire is challenging lattice and symmetry mismatch. In this study, β-Ga₂O₃ thin films were grown on C-plane sapphire substrates with various off-axis angles (0–12°) using mist-CVD, and the influence of substrate miscut on structural and optical properties was investigated. All films grown at 900°C exhibited (-201) oriented β phase. The crystal quality was strongly dependent on the off-axis angle, with intermediate off-axis angles (Δ_a = 6–8°) showing the narrowest rocking curve width. Off-axis substrates promoted step-aligned growth behavior compared to on-axis growth. Optical measurements revealed enhanced transmittance and wider bandgap values (4.92–4.95 eV) for off-axis samples compared to the on-axis film (4.69 eV). The findings provide practical guidelines for optimizing heteroepitaxial β-Ga₂O₃ growth on low-cost sapphire substrates for high-performance device applications.

κ-phase Ga₂O₃ is a wide-bandgap semiconductor that has attracted attention for power and optoelectronic device applications. However, its crystal quality and optical properties are highly dependent on the growth temperature, which motivates the need for a systematic study. In this work, κ-Ga₂O₃ thin films were grown on AlN/sapphire templates using mist-CVD at different temperatures. At lower temperatures (400℃), films exhibited incomplete crystallization and partial opacity, whereas higher growth temperatures (500-700℃) produced transparent films with improved properties. The bandgap was found to increase with temperature, consistent with reported values for 600-700℃, and XRD/XRC analysis confirmed that crystal quality improved with higher growth temperature. AFM analysis further revealed reductions in surface roughness and grain size variation at elevated temperatures. These findings indicate that an optimal growth window of 600-700℃ enables high-quality κ-Ga₂O₃ films, with potential implications for integrating this material on other hexagonal substrates such as SiC and GaN.