Nanostructured Surface Morphology of ZnO Grown On A-plane GaN

ZnO nanostructures were grown on a-plane GaN templates by chemical vapor deposition (CVD) without employing a catalyst. The a-plane GaN templates were pre-deposited on an r-plane sapphire substrate by metal-organic CVD. For the 800{degree sign}C-grown sample, a ZnO layer with a thickness of 0.1 μm was formed by grains with a size of about 40 nm. For the 900oC-grown sample, ZnO nanowires were grown in angles off-related to the GaN basal plane with a ZnO layer between wires and template formed by grains with a size of about 300 nm. X-ray diffraction spectra showed that the ZnO layer was grown with a heteroepitaxial relationship of (110)ZnO||(110)GaN. The growth mechanism on a-plane GaN was the Volmer-Weber mode and differed from the Stranski-Krastanow mode observed for growth on c-plane GaN. This difference results from the higher interfacial free-energy on the a-plane between ZnO and GaN than that on the c-plane orientation.