Synthesis and photoluminescence of ZnO nanowires/nanorods

We report growth of ZnO nanowires on various substrates using a vapour phase transport method and show that the growth mechanism is vapour-liquid-solid growth. We present photoluminescence data for samples grown on a-plane sapphire at room and low temperatures indicating that the optical quality of these structures is potentially excellent, with intense emission and narrow bound exciton linewidths. The intensity decays rapidly with increasing temperature, indicating a strong temperature-activated non-radiative mechanism whose origin is unclear. We observe a high energy excitonic emission close to the band edge which we assign to the “surface” exciton in ZnO at ∼3.368 eV. This assignment is consistent with the large surface to volume ratio of the nanowire systems under consideration and also indicates that this large ratio has a significant effect on the luminescence even at low temperatures. These surface effects may also be responsible for the rapid decay of the luminescence with increasing temperature via a temperature-activated surface recombination. The nanowire systems appear to offer the prospect of extremely efficient excitonic emission for device applications, and we note that one of the important aspects of achieving this potential will be control of the surface effects via passivation or other means.