High-quality ZnO/GaN/Al₂O₃ heteroepitaxial structure grown by LP-MOCVD

High-quality ZnO films were grown on epi-GaN predeposited on c-Al ₂O₃ substrates using low-pressure metal-organic chemical vapor deposition (MOCVD). Detailed study of the X-ray diffraction spots and patterns by different diffractometers showed high structural perfection of the zinc oxide layer, which indicated that the growth of ZnO film was strongly c-oriented. The full-width at half-maximum (FWHM) of the ω-rocking curve was 0.39°. Surface morphology of the films studied by AFM showed that the growth of the ZnO film followed the regular hexagonal column structure with about 500nm grain diameter. Zn and O elements in the deposited ZnO/GaN/Al ₂O₃ films were investigated and compared by X-ray photoelectron spectroscopy (XPS), in which the dissociative O and Zn atom peak was hardly observed. The ratio of O/Zn atoms of the film was about 1 with O-rich. Photoluminescence spectra of the ZnO films grown on epi-GaN showed dominating exciton emission peak, and the deep-level emission which was obvious on ZnO/Al₂O₃ film had hardly been observed.