Incorporation of indium into ε-gallium oxide epitaxial thin films grown via mist chemical vapour deposition for bandgap engineering

Abstract

Epitaxial ε-gallium oxide (Ga₂O₃) thin films incorporated with In were successfully grown by mist chemical vapour deposition (CVD) on c-plane sapphire substrates for bandgap tuning. In was successfully incorporated into epitaxial ε-(In_xGa_1−x)₂O₃ films at an In composition of x = 0.2 without inducing phase separation. Phase separation originated from the (400) bixbyite structure of (In_xGa_1−x)₂O₃ when x > 0.2. The solubility limit of In incorporated into ε-Ga₂O₃ on sapphire substrates via mist CVD was therefore x = 0.2. Transmission electron microscopy measurements revealed that ε-(In_xGa_1−x)₂O₃ consisted of polycrystalline phases observed in the interface of the sapphire substrate and ε-phases located above the polycrystalline phase. The pole figure of ε-(In_xGa_1−x)₂O₃ thin films revealed that the epitaxial relationship between the ε-(In_xGa_1−x)₂O₃ thin film and the α-Al₂O₃ substrate is (001) ε-(In_xGa_1−x)₂O₃ [130]||(0001) α-Al₂O₃ [11−20]. The optical bandgap of the ε-(In_xGa_1−x)₂O₃ thin films was tuned from 4.5 to 5.0 eV without inducing phase separation.