Visible Photoluminescence Components of Solution-Grown ZnO Nanowires: Influence of the Surface Depletion Layer

Arrays of electrodeposited ZnO nanowires (NWs) were used to illustrate the dependence of the ZnO visible photoluminescence (PL) emission on the extension of the surface depletion layer and obtain further insight into the localization of the related states. With this goal in mind, three sets of measurements were carried out: (i) analysis of the PL spectra of ZnO:Cl NWs as a function of their carrier concentration; (ii) analysis of the PL spectra of ZnO:Cl/ZnO core-shell NWs as a function of the thickness of their intrinsic ZnO shell; (iii) in situ analysis of the PL dependence on the polarization of ZnO:Cl photoelectrodes. The obtained experimental results evidenced that the yellow and orange emissions from electrodeposited ZnO NWs are correlated with the extension of the NWs surface depletion region. This result points out the surface localization of the states at the origin of these transitions. On the other hand, the green emission that dominates the visible part of the PL spectra in annealed ZnO NWs showed no dependence on the surface band bending, thus pointing toward its origin in the bulk.