Controlled growth of two-dimensional ZnO nanowalls by thermal chemical vapor deposition

Morphology and crystallographic properties of two-dimensional ZnO nanowalls epitaxially grown on catalytic Au-deposited GaN/c-plane sapphire substrates in a thermal chemical vapor deposition process were studied as a function of growth temperature. Vertically well-aligned ZnO nanowall networks with different wall size and morphology were formed at 880, 900 and 920 degrees C, respectively. We observed that the ZnO nanowall networks were of a single-crystalline structure and showed a perfect epitaxial relation with the catalytic An and the GaN substrate in high-resolution electron microscopy and synchrotron X-ray scattering experiments. It was found that the crystal quality of ZnO nanowall and catalytic An was improved with increasing growth temperature in X-ray powder diffraction measurements. The room-temperature photoluminescence spectrum showed a quite strong and sharp ultraviolet emission as well as relatively weak deep-level emission, indicating good optical properties of the ZnO nanowall samples in this work.