Mechanisms for high internal quantum efficiency of ZnO nanorods

We investigate the photoluminescence properties of ZnO nanorods grown by vapor phase epitaxy. The room temperature photoluminescence spectra exhibit an energy shift of about 80 meV to lower energy in comparison with that of bulk ZnO as well as ZnO epilayers. The emission band observed at 3.31 eV at low temperature dominates the photoluminescence at room temperature. The high internal quantum efficiency of about 33% is explained in terms of this band, which seems to result from excitons bound to surface defect states.