Spectral investigation of carrier recombination processes in ZnO nanorods at high temperatures

The mechanism of near-band-edge (NBE) emission from crystalline ZnO (c-ZnO) nanorods grown on c-Si by a catalyst-assisted vapor-liquid-solid method has been investigated by performing temperature-, power-, and time-dependent photoluminescence (PL) measurements at a temperature (T) range of 143-503 K. In contrast to previous reports, we find that the NBE PL is primarily associated with free exciton emission, whereas the contribution of band-to-band and free-to-bound radiative recombinations remains negligible up to the highest T studied. A spectral evolution of the NBE band with T was further analyzed within the framework of a three-parameter model, proposed recently, with the results presented and discussed. Finally, the ratio of excitonic-to-defect luminescence intensity has been observed to change nonmonotonically with T, which is explained based on the difference in the quenching mechanisms of exciton and defect PL. (C) 2008 American Institute of Physics.