Control of Crystal Structure of Ga2O3 on Sapphire Substrate by Introduction of α‐(AlxGa1−x)2O3 Buffer Layer

Abstract

An annealed α‐(Al0.4Ga0.6)2O3 buffer layer is introduced to achieve either α‐Ga2O3 or ϵ‐Ga2O3 growth on sapphire substrates, depending on the growth temperature, using the mist chemical vapor deposition method. Transmission electron microscopy reveals that the epitaxial relationship between ϵ‐Ga2O3 and the α‐(Al0.4Ga0.6)2O3 buffer layer is ϵ‐Ga2O3 [100] || α‐(Al0.4Ga0.6)2O3 [110], and the two hexagonal lattices are consequently rotated in the ab plane by 30° with respect to each other. The lattice mismatch between the buffer layer and ϵ‐Ga2O3 is 1.2%, while that between the buffer layer and α‐Ga2O3 is 2.2%. When the growth temperature is below 600 °C, ϵ‐Ga2O3, which had the smaller lattice mismatch, is produced. On the other hand, higher temperature leads to a longer diffusion length, and atoms reach the step edges. Therefore α‐Ga2O3, which has the same structure as the buffer layer, is grown along the step edges above 600 °C. As a result, ϵ‐Ga2O3 and α‐Ga2O3 grow below and above 600 °C, respectively.