Investigation of Ga oxide films directly grown on n-type GaN by photoelectrochemical oxidation using He-Cd laser

By using a He-Cd laser in a chemical solution of H3PO4 with a pH value of 3.5, Ga oxide films were directly grown on n-type GaN. From the energy-dispersive spectrometer (EDS) measurement and x-ray diffraction (XRD) measurement, the grown Ga oxide film was identified as (104) alpha-Ga2O3 structure. A small amount of phosphors existed and bonded with oxygen on the grown films. The as-grown films were amorphous. From the XRD analysis, it is evident that annealing of the alpha-Ga2O3 films led to a change in the microstructure from an amorphous to a polycrystalline phase. In addition, the as-grown low-density films gradually became dense films during the annealing process. Furthermore, the surface roughness of the annealed films also gradually decreased. Hexagonal pinholes on the grown films were observed. The density of the hexagonal pinholes was similar to the defect density of the n-type GaN. From the cross-sectional transmission electron microscopy (TEM) micrographs, it is evident that the hexagonal pinholes originated from defects in the n-type GaN.