ZnO nanoneedles with enhanced and sharp ultraviolet cathodoluminescence peak

Tapered ZnO nanorod, herein called nanoneedle, arrays have been grown on ZnO-coated silicon substrate by a hydrothermal downward growth process. The ZnO seed layer facilitated the growth of aligned nanorods. The nationeedles were (,town with the substrate placed flush with the surface of the reaction solution and facing downward. The correlation between the depletion of solution and reaction temperature was exploited to control the length of the tapered portion of ZnO nanoneedles for the same solution. The vertical ZnO nanoneedle arrays exhibit very strong and sharp ultraviolet emission from band gap transition and almost no green emission attributed to singly ionized oxygen vacancies in the cathdoluminescence spectrum. The enhancement in optical properties will be advantageous in applications for nanoscale light-emitting devices.