Microstructural analysis of heteroepitaxial β-Ga₂O₃ films grown on (0001) sapphire by halide vapor phase epitaxy

($\overline{2}$01)-oriented β-Ga₂O₃ films have been grown on (0001) sapphire substrates using the halide vapor phase epitaxy method. The as-grown β-Ga₂O₃ films exhibit highly textured with domain-like surface morphologies and the root-mean-square roughness is measured at 6.2 nm using atomic force microscopy. The microstructure characteristics of the β-Ga₂O₃ film have been investigated comprehensively to understand the origin for the domain-like morphologies. Two in-plane rational domains with mirror-symmetrical atomic arrangement have been identified along the [010] axis of β-Ga₂O₃ by high resolution transmission electron microscopy, which are caused by the (0001) sapphire substrate symmetry. Various defects, including twinned crystals, inversion domains and domain boundaries etc, have been observed, leading to the rough surfaces and poor crystalline quality of β-Ga₂O₃ grown on non-angled (0001) sapphire substrate. Schematic diagrams and the oxygen atomic arrangements of β-Ga₂O₃ on ∼7° off-angled (0001) sapphire substrate toward the 〈11$\overline{2}$0〉 plane were proposed to illustrate the in-plane quasi-epitaxial relationships between the β-Ga₂O₃(400) film and the sapphire (11$\overline{2}$3) substrate, and to explain the single domain growth mechanism. The results would be helpful for improving the surface morphologies and crystalline quality of heteroepitaxial Ga₂O₃ films. (paper)