Study of the Photoluminescence Enhancement Observed in ZnO Nanowire Gratings Optimally Grown by the Hydrothermal Method

An original ZnO nanowire (NW) architecture has been developed, entirely based on a soft chemistry approach, and thoroughly assessed through optical measurements and electromagnetic simulations. This architecture relies on the photoimprinting of a sol-gel ZnO-based photosensitive seed layer combined with the subsequent localized hydrothermal growth of ZnO NWs. The optimization of the elaboration protocol has been shown to lead to uniform and reproducible linear and periodic gratings of ZnO NWs with a width/pitch of 2/4 & mu;m. The NW gratings are compared with full-covered samples (NWs coating) elaborated from a nonimprinted seed layer. A morphological study reveals that NW gratings present a peculiar hedgehog-like profile. Standard and angle-resolved photoluminescence studies demonstrate that the ZnO NWs visible emission is strongly modified by the presence of NW gratings and that its red part is directionally extracted and enhanced by a factor of up to 2. The electromagnetic simulations performed for both samples highlight the role of the gratings acting as coupled microcavities that boost the ZnO emission through light localization and diffractive mechanisms. It enables the extraction of the resonant photons at specific angles and wavelengths.