In this study, κ-Ga₂O₃ thin films were heteroepitaxially grown on GaN templates using metal-organic chemical vapor deposition (MOCVD), and the effects of growth conditions and nucleation layer structures on phase formation and crystalline quality were systematically investigated. Under direct growth conditions, increasing the growth temperature and H₂O flow rate led to the incorporation of the β-Ga₂O₃ phase. In particular, mixed κ + β phases were observed at elevated temperatures above 680 °C. To suppress β-phase formation and maintain a single κ phase, a two-step growth method was employed, and the influence of nucleation layer thickness and structure on the crystalline quality was comparatively analyzed. As a result, the 100 nm-thick κ-Ga₂O₃ nucleation layer exhibited improved surface coalescence and a reduced threading dislocation density, effectively suppressing β-phase formation even under high-temperature epitaxial conditions. Φ-scan analysis further confirmed the presence of three-fold rotational domains in the κ-Ga₂O₃ films and revealed an in-plane epitaxial relationship of κ-Ga₂O₃ (201) // GaN (11-20). Additionally, the maximum growth temperature at which a single-phase κ-Ga₂O₃ could be maintained was identified to be 720 °C. These findings propose an effective approach for the stable growth of single-phase κ-Ga₂O₃ thin films at elevated temperatures.

Keywords: MOCVD, Ga₂O₃, Crystal phase, Structural evolution, GaN/Si template.