Growth Pressure Controlled Nucleation Epitaxy of Pure Phase epsilon- and beta-Ga2O3 Films on Al2O3 via Metal-Organic Chemical Vapor Deposition

Pure epsilon- and beta-phase gallium oxide (Ga2O3) films have been successfully grown on Al2O3 (001) substrate via metal-organic chemical vapor deposition (MOCVD) at a growth temperature of 500 degrees C. Growth pressure controlled nucleation is the dominant controlling parameter for pure phase Ga2O3 film growth. Due to the biaxial stress induced by lattice mismatch, heteroepitaxial epsilon-phase Ga2O3 is grown on Al2O3 by heterogeneous nucleation at low pressure. However, film growth is dominated by spherical nuclei homogeneous nucleation at a pressure higher than 100 mbar, and beta-phase Ga2O3 film is grown with a mosaic surface. The optimum pressure for the growth of pure epsilon-Ga2O3 films with superior crystallinity is 35 mbar, whereas the pressure window for pure beta-Ga2O3 growth is between 100 mbar and 400 mbar. The growth rate of beta-Ga2O3 film is much lower than epsilon-Ga2O3 film at high pressure. On the other hand, all. Ga2O3 films have shown good optical properties with a band gap of about 4.9 eV. This fundamental research will help to understand the mechanism of MOCVD growth involving high quality and pure phase epsilon- and beta-Ga2O3 film.