Cathodoluminescence study of single zinc oxide nanopillars with high spatial and spectral resolution

Abstract

Single zinc oxide (ZnO) nanopillars grown by the vapor-liquid-solid process on a-plane sapphire are investigated by spatially resolved cathodoluminescence on the nanometer scale in a scanning electron microscope. Spectra were recorded by exciting luminescence along single pillars and across the underlying wetting layer. Luminescence from the excited pillar spots exhibited sharp bound exciton lines and intrinsic free-exciton recombination, whereas the wetting layer showed only very weak luminescence. Along the pillars, virtually no shift of the lines was observed. This is interpreted as evidence for strain-free growth of the pillars. In the bottom region of the pillars aluminum incorporation from the substrate material was found. There are indications for an incorporation of gallium along the pillars due to unintentional doping introduced by the source material. The spot-resolved results are compared to integral photoluminescence measurements with large-area excitation carried out on the same sample region.