Synthesis of High-Quality α-Ga₂O₃ thin films on Sapphire Substrates with Introduction of Buffer Layers

Abstract

Corundum-structured gallium oxide (α-Ga₂O₃) on sapphire substrates is advantageous in views of band gap engineering and low-cost, but heterogeneous phases and rotation domains tend to be included owing to the heteroepitaxy. The insertion of α-(Al_xGa_1-x)₂O₃ alloy buffer layers was effective for their elimination. This paper showed the elimination of heterogeneous phases (especially the β-Ga₂O₃ phase) and rotational domains, which have been often seen in α-Ga₂O₃ thin films on c-plane sapphire substrates with the use of α-(Al_xGa_1-x)₂O₃ buffer layers. These results are attributed to the stress reduction in α-Ga₂O₃ grown on the underlying layer. This was done without modifying the growth conditions, that is, without narrowing the windows of growth conditions. This result also suggests the important role of any buffer layers on sapphire substrates in order for further improvements of crystal quality of α-Ga₂O₃, leading to evolution of a variety of Ga₂O₃-based devices on low-cost and large-area on sapphire substrates.