Comparison of the optical properties of as-grown ensembles and single ZnO nanowires

By use of micro-photoluminescence spectroscopy we analyze and compare the optical properties of individual zincoxide nanowires, with diameters 90 nm < d < 620 nm, and of the as-grown ensemble. After special preparation techniques individual nanowires of different morphologies and crystalline qualities are observed which possess distinctively different near band-edge excitonic features. We show that the spectral shape of these excitonic emission lines correlates with the morphology of the nanowires. Our results clearly show that for decreasing wire diameter, distinct surface-related spectral features strongly contribute to the optical properties of individual ZnO nanowires. Finally, the temperature dependence of the near band-edge emission is analyzed. The results obtained from individual wires provide information about the homogeneity of the optical properties of the wires in the as-grown ensembles, and show that easily performed ensemble measurements indeed reflect the properties of typical individual, single nanowires.