Evidence for low density of nonradiative defects in ZnO nanowires grown by metal organic vapor-phase epitaxy

Low temperature cathodoluminescence and temperature dependent time resolved photoluminescence are used to investigate the emission properties of ZnO nanowires grown by metal organic vapor phase epitaxy. Low temperature cathodoluminescence images show that the emission process is more efficient in ZnO nanowires than in the underlying two dimensional layer. Temperature dependent photoluminescence spectra and decay time measurements give a detailed insight on the role of the donor bound exciton, the free exciton, and the nonradiative channels in the emission process. In particular, it is shown that up to room temperature, the escape toward nonradiative channels is limited because of the very low defect density in the ZnO nanowires.