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

Pure ε- and β-phase gallium oxide (Ga 2 O 3 ) films have been successfully grown on Al 2 O 3 (001) substrate via metal–organic chemical vapor deposition (MOCVD) at a growth temperature of 500 °C. Growth pressure controlled nucleation is the dominant controlling parameter for pure phase Ga 2 O 3 film growth. Due to the biaxial stress induced by lattice mismatch, heteroepitaxial ε-phase Ga 2 O 3 is grown on Al 2 O 3 by heterogeneous nucleation at low pressure. However, film growth is dominated by spherical nuclei homogeneous nucleation at a pressure higher than 100 mbar, and β-phase Ga 2 O 3 film is grown with a mosaic surface. The optimum pressure for the growth of pure ε-Ga 2 O 3 films with superior crystallinity is 35 mbar, whereas the pressure window for pure β-Ga 2 O 3 growth is between 100 mbar and 400 mbar. The growth rate of β-Ga 2 O 3 film is much lower than ε-Ga 2 O 3 film at high pressure. On the other hand, all Ga 2 O 3 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 ε- and β-Ga 2 O 3 film.