Defect-related energy structures of AlN nanotips probed by photoluminescence

Large-scale AlN nanotip arrays were fabricated via a facile catalysis-free approach using AlCl3 powder and NH3 as starting materials. These nanotips exhibit two intense broad emissions centred at about 375 and 480 nm. Both bands do not change significantly or freeze out at a low temperature, showing the features of photoionization of deep donor electrons. Photoluminescence and photoluminescence excitation spectral examination as well as the possible mechanism involved are systematically investigated. It reveals that the two bands are connected with the electronic states determined by the nitrogen vacancy and complex defects. The related energy structures are also provided. This work provides a possible mechanism for defect-related emissions in various AlN nanostructures.