Formation of High-Quality Heteroepitaxial β-Ga₂O₃ Films by Crystal Phase Transition

Sn-doped ɛ-phase dominant Ga₂O₃ films (ɛ-Ga₂O₃ films) are grown on c-plane sapphire substrates using metal–organic vapor-phase epitaxy and transformed to β-phase films by thermal annealing. The morphological and electrical properties of the phase-transformed β-Ga₂O₃ films dependent on experimental conditions are characterized. The ɛ-Ga₂O₃ film is completely transformed to the β-phase by thermal annealing to realize a high electrical conductivity while maintaining a good surface flatness. When the ɛ-Ga₂O₃ films are grown, a mixing ratio of the β-Ga₂O₃ component to the ɛ-Ga₂O₃ film is controlled to improve the crystalline quality of the β-Ga₂O₃ films transformed from ɛ-Ga₂O₃ by annealing (transformed β-Ga₂O₃). Compared to an as-grown β-Ga₂O₃ film, higher-quality heteroepitaxial β-Ga₂O₃ films with better electrical conductivity and surface morphology can be obtained by the phase transition method, and these results show adequate repeatability.