Surface morphology of homoepitaxial β-Ga2O3 thin films grown by molecular beam epitaxy

β-Ga2O3 thin films were grown on (100)-oriented β-Ga2O3 single crystal substrates by plasma-assisted molecular beam epitaxy. At the growth temperature over 800 °C and the Ga beam equivalent pressure of 1.1 × 10− 7 Torr, the grown surfaces exhibited clear step and terrace structures and the root-mean-square roughness of 0.5 nm in atomic force microscopy. The successful step-flow growth is indebted to the strong cleavableness of (100) planes of β-Ga2O3. The off-axis direction, determined by the initial substrate polishing stage, significantly influences on the surface morphology, and it should be along [001] or [00-1] directions in order for smooth surfaces.