Epitaxial growth of γ-(AlxGa1-x)2O3 alloy thin films on spinel substrates via mist chemical vapor deposition

Highlights:• Alloying γ-Ga₂O₃ and γ-Al₂O₃ effective for lattice-matched growth on spinel substrate.• Demonstrated epitaxial growth of γ-(Al_xGa_1-x)₂O₃ alloy thin films using mist CVD.• Band gap engineering achieved for 5.0–6.0 eV by estimating direct band gap energy. -- Abstract: Among the five polymorphs of α, β, γ, δ, and κ(ε)-gallium oxide (Ga₂O₃), we focused on metastable cubic γ-Ga₂O_3, which exhibits a defect spinel structure, from the viewpoint of lattice matching. Alloying γ-Ga₂O₃ with γ-aluminum oxide (γ-Al₂O₃), which exhibits the same crystal structure as that of the former, is effective for lattice-matched growth on a spinel substrate as well as band gap engineering. At the composition ratio x = 0.48, γ-aluminum gallium oxide (γ-(Al_xGa_1-x)₂O₃) lattice matched to the spinel substrate, and its band gap energy increased to 5.88 eV. Thus, γ-(Al_xGa_1-x)₂O₃ is a promising material for wide band gap semiconductors that are lattice matched to the substrates, for applications in power-switching devices and deep-ultraviolet optoelectronics. In this study, we demonstrated the epitaxial growth of γ-(Al_xGa_1-x)₂O₃ alloy thin films on spinel substrates using mist chemical vapor deposition. At the Al concentration of 0.11 M, the epitaxial γ-(Al_xGa_1-x)₂O₃ thin film was successfully grown with Laue-oscillations observed in the X-ray diffraction 2θ–ω scan. Moreover, transmission electron microscopy measurements revealed that the γ-(Al_xGa_1-x)₂O₃ thin film was lattice matched and grown on the spinel substrate with few misfit dislocations at the interface. Band gap engineering was achieved in the range of 5.0–6.0 eV by estimating the direct band gap energy. Thus, our results, which indicate the possibility of limited dislocations due to lattice matches, are expected to facilitate the development of materials with wider band gaps based on γ-(Al_xGa_1-x)₂O₃.