Research Highlights

Growth, catalysis, and faceting of α-Ga₂O₃ and α-(InₓGa₁₋ₓ)₂O₃ on m-plane α-Al₂O₃ by molecular beam epitaxy

Martin S. Williams, Manuel Alonso-Orts, Marco Schowalter, Alexander Karg, Sushma Raghuvansy, Jon P. McCandless, Debdeep Jena, Andreas RosenauerMartin Eickhoff, Patrick Vogt 

APL Materials 12 (2024): 011120

https://doi.org/10.1063/5.0180041

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).

Growth, catalysis, and faceting of α-Ga2O3 and α-(InxGa1−x)2O3 on m-plane α-Al2O3 by molecular beam epitaxy pic
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