Orientation-Dependent Atomic-Scale Mechanism of β-Ga_2O_3 Thin Film Epitaxial Growth

β-Ga_2O_3 has gained intensive interests of research and application as an ultrawide bandgap semiconductor. Epitaxial growth technique of the β-Ga_2O_3 thin film possesses a fundamental and vital role in the Ga_2O_3-based device fabrication. In this work, epitaxial growth mechanisms of β-Ga_2O_3 with four low Miller-index facets, namely (100), (010), (001), and (201), are systematically explored using large-scale machine-learning molecular dynamics simulations at the atomic scale. The simulations reveal that the migration of the face-centered cubic stacking O sublattice plays a predominant role in rationalizing the different growth mechanisms between (100)/(010)/(001) and (201) orientations. The resultant complex combinations of the stacking faults and twin boundaries are carefully identified, and shows a good agreement with the experimental observation and ab initio calculation. Our results provide useful insights into the gas-phase epitaxial growth of the β-Ga_2O_3 thin films and suggest possible ways to tailor its properties for specific applications.