Cathodoluminescence characterization of ZnO nanotubes grown by MOCVD on sapphire substrate

Cathodoluminescence (CL) imaging and spectroscopy was used to study ZnO hexagonal nanotubes fabricated by metalorganic chemical vapor deposition on sapphire (0 0 0 1) substrate. The CL spectra at room temperature and low temperature showed that the ZnO nanotubes were incorporated with acceptors. Top-view CL images showed an enhanced emission from the tubes. The side-view CL image and CL spectra of different points from a single nanotube showed that ultraviolet emission became weaker and shifted to shorter wavelength along the growth direction of the nanotube. These results were explained by the unintentional impurity doping during the growth process.