β-Ga2O3 epitaxial films deposited on epi-GaN/sapphire (0001) substrates by MOCVD

Gallium oxide (Ga2O3) films were grown on epi-GaN/sapphire (0001) substrates by the metalorganic chemical vapor deposition (MOCVD) method, followed by a post-deposition thermal annealing at different temperatures of 800, 900 and 1000 ℃ for one hour in air. X-ray diffraction (XRD, both θ~2θ and Φ scans) and transmission electron microscopy (TEM) were used to inspect the lattice structure and epitaxial relationship. With the increase of annealing temperature, the film structure changed from amorphous to single crystalline and then to polycrystalline. A single crystalline β-Ga2O3 film with the best crystalline quality was obtained under the annealing condition at 900 ℃, and a clear epitaxial relationship of β-Ga2O3(100)‖GaN(0001) with β-Ga2O3 < 010 > ‖GaN < 1¯21¯0 > and β-Ga2O3 < 001 > ‖GaN < 1¯010 > was determined. The elemental composition and proportion of the 900 ℃-annealed film were investigated by the X-ray photoelectron spectroscopy (XPS) measurements and the atomic ratio of Ga/O was about 0.69, which was close to stoichiometric Ga2O3. For the sample annealed at 900 ℃, the average transmittance in the visible wavelength region was about 78% and the average reflectivity in the 200-800 nm wavelength range was about 18%.