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The growth of α-Ga2O3 and α-(InxGa1−x)2O3 on m-plane α-Al2O3(101̄0) by molecular beam epitaxy (MBE) and metal-oxide-catalyzed epitaxy (MOCATAXY) is investigated. By systematically exploring the parameter space accessed by MBE and MOCATAXY, phase-pure α-Ga2O3(101̄0) and α-(InxGa1−x)2O3(101̄0) thin films are realized. The presence of In on the α-Ga2O3 growth surface remarkably expands its growth window far into the metal-rich flux regime and to higher growth temperatures. With increasing O-to-Ga flux ratio (RO), In incorporates into α-(InxGa1−x)2O3 up to x ≤ 0.08. Upon a critical thickness, β-(InxGa1−x)2O3 nucleates and, subsequently, heteroepitaxially grows on top of α-(InxGa1−x)2O3 facets. Metal-rich MOCATAXY growth conditions, where α-Ga2O3 would not conventionally stabilize, lead to single-crystalline α-Ga2O3 with negligible In incorporation and improved surface morphology. Higher TTC further results in single-crystalline α-Ga2O3 with well-defined terraces and step edges at their surfaces. For RO ≤ 0.53, In acts as a surfactant on the α-Ga2O3 growth surface by favoring step edges, while for RO ≥ 0.8, In incorporates and leads to a-plane α-(InxGa1−x)2O3 faceting and the subsequent (2̄01) β-(InxGa1−x)2O3 growth on top. Thin film analysis by scanning transmission electron microscopy reveals highly crystalline α-Ga2O3 layers and interfaces. We provide a phase diagram to guide the MBE and MOCATAXY growth of single-crystalline α-Ga2O3 on α-Al2O3(101̄0).

The heteroepitaxial growth and phase formation of Ga2O3 on Al-polar AlN(0001) templates by molecular-beam epitaxy (MBE) are studied. Three different MBE approaches are employed: (i) conventional MBE, (ii) suboxide MBE (S-MBE), and (iii) metal-oxide-catalyzed epitaxy (MOCATAXY). We grow phase-pure β-Ga2O3(2̄01) and phase-pure ϵ/κ-Ga2O3(001) with smooth surfaces by S-MBE and MOCATAXY. Thin film analysis shows that the crystallographic and surface features of the β-Ga2O3(2̄01)/AlN(0001) and ϵ/κ-Ga2O3(001)/AlN(0001) epilayers are of high crystalline quality. Growth and phase diagrams are developed to synthesize Ga2O3 on AlN by MBE and MOCATAXY and to provide guidance to grow Ga2O3 on several non-oxide surfaces, e.g., AlN, GaN, and SiC, by MBE, S-MBE, and MOCATAXY.