Pseudomorphic growth of Si-doped -(AlGa)₂O₃ on m-plane a-Al₂O₃ substrates by molecular beam epitaxy

alpha-(AlGa)(2)O-3 is an attractive material for high-power devices and vacuum UV optoelectronics. However, alpha-(AlGa)(2)O-3 on sapphire substrates suffers from lattice relaxation and phase transformation. Here, we investigated the effect of controlling the Al composition and thickness of Si-doped alpha-(AlGa)(2)O-3 layers pseudomorphically grown on alpha-Al2O3 (10(1)0) substrates by MBE. We found that the critical layer thicknesses of alpha-(AlGa)(2)O-3 layers with Al compositions of 58%, 66%, and 79% were around 13, 18, and 44 nm, respectively. We also found that a 9.0 nm thick alpha-(Al0.65Ga0.35)(2)O-3 /3.5 nm thick Al2O3 multilayer with 20 periods grew almost pseudomorphically and formed alpha-(Al0.90Ga0.10)(2)O-3 alloy after post-thermal annealing at 1400 degrees C. (C) 2023 The Japan Society of Applied Physics