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

An annealed -(Al0.4Ga0.6)(2)O-3 buffer layer is introduced to achieve either -Ga2O3 or E-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 E-Ga2O3 and the -(Al0.4Ga0.6)(2)O-3 buffer layer is E-Ga2O3 [1010] || -(Al0.4Ga0.6)(2)O-3 [110], and the two hexagonal lattices are consequently rotated in the ab plane by 30 degrees with respect to each other. The lattice mismatch between the buffer layer and E-Ga2O3 is 1.2%, while that between the buffer layer and -Ga2O3 is 2.2%. When the growth temperature is below 600 degrees C, E-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 -Ga2O3, which has the same structure as the buffer layer, is grown along the step edges above 600 degrees C. As a result, E-Ga2O3 and -Ga2O3 grow below and above 600 degrees C, respectively.