Ordered ZnO nanorod arrays with almost uniform rod size have been grown perpendicularly on GaN/Al2O3 substrates by a controlled vapor phase transport growth method. The ZnO nanorods are  oriented single crystals with diameter of 200 nm and length of 4.7 µm, with a rod-to-rod spacing of 500 nm. Photoluminescence spectra of the rod arrays indicate that the rods are of high crystal quality: very strong, well-separated bound and free exciton emission in the ultraviolet (UV) region are resolved at low temperature. Time resolved microphotoluminescence measurements are performed on single nanorods standing on the substrate which demonstrates lasing behavior with multiple UV lasing modes. Under quasistationary excitation lasing is observed up to room temperature. The lasing emission peaks are sharp, with a linewidth about 0.1 nm, and have a fast decay time of ~8 ps. These high crystal quality nanorod arrays may be promising candidates for UV nanolaser devices.
H. Zhou, M. Wissinger, J. Fallert, R. Hauschild, F. Stelzl, C. Klingshirn, H. Kalt
Appl. Phys. Lett. 91, 181112 (2007)