Strong ultraviolet luminescence of ZnO thin films with nanowall-network structures

ZnO thin films with three different types of surface structures, smooth, large nanowall-networks, and small nanowall-networks, were grown by a vapor phase transport process. The XRD patterns of these samples showed a high c-axis orientation. Photoluminescence spectra of these samples showed that the intensities of ultraviolet (UV) emission from ZnO thin films having a surface with nanowall-network structures were enhanced by 1-2 orders of magnitude, the linewidths of UV emission were reduced, and the peak positions blueshifted significantly compared with the ZnO film having a smooth surface. The greatly enhanced UV emission was attributed to high crystalline quality with the oriented growth, and whispering gallery mode resonance in the nanowall-formed cavities.