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In this paper, hexagonal structure phase-pure wide-band gap ε-Ga2O3 films were grown by metal organic chemical vapor deposition on 6H-SiC substrates. The ε-Ga2O3 films with good crystal quality were verified by high-resolution X-ray diffraction. The out-of-plane epitaxial relationship between ε-Ga2O3 films and 6H-SiC substrates is confirmed to be ε-Ga2O3 (0001)//6H-SiC (0001), and the in-plane epitaxial relationship is also confirmed to be ε-Ga2O3 ⟨112¯0⟩//6H-SiC ⟨112¯0⟩. The SEM and AFM images show that the ε-Ga2O3 films are uniform and flat. The ε-Ga2O3 films are thermally stable up to approximately 800 °C and begin to transform into β-phase Ga2O3 at 850 °C. Then, they are completely converted to β-Ga2O3 films under 900 °C. The high-quality ε-Ga2O3 films with hexagonal structure have potential application in the optoelectronic field.

Pure ε- and β-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 °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 ε-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 β-phase Ga2O3 film is grown with a mosaic surface. The optimum pressure for the growth of pure ε-Ga2O3 films with superior crystallinity is 35 mbar, whereas the pressure window for pure β-Ga2O3 growth is between 100 mbar and 400 mbar. The growth rate of β-Ga2O3 film is much lower than ε-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 ε- and β-Ga2O3 film.