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

Abstract

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).

Step-edge-guided nucleation and growth mode transition of α-Ga2O3 heteroepitaxy on vicinal sapphire

“…Despite of these promising advantages, α-Ga 2 O 3 can be only achieved on foreign substrates due to its metastable nature, and the misfit strain leads to much higher threading dislocation densities than those in β -Ga 2 O 3 homoepitaxial layer. [10][11][12] These harmful defects typically result in significant carrier compensation and mobility degradation, inevitably leading to an increase in reverse leakage current and premature power device breakdown. [9,[13][14][15][16] Owing to the significant potential of α-Ga 2 O 3 as previously noted, various growth equation methods have been employed for heteroepitaxial growth of α-Ga 2 O 3 on sapphire substrates, including halide vapor phase epitaxy (HVPE), metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), metal-organic vapor phase epitaxy (MOVPE), and mist chemical vapor deposition (Mist-CVD).…”