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We investigate the origin of the fast recombination dynamics of bound andfree excitons in GaN nanowire ensembles by temperature-dependentphotoluminescence spectroscopy using both continuous-wave and pulsedexcitation. The exciton recombination in the present GaN nanowires is dominatedby a nonradiative channel between 10 and 300 K. Furthermore, bound and freeexcitons in GaN NWs are strongly coupled even at low temperatures resulting ina common lifetime of these states. By solving the rate equations for a coupledtwo-level system, we show that one cannot, in practice, distinguish whether thenonradiative decay occurs directly via the bound or indirectly via the freestate. The nanowire surface and coalescence-induced dislocations appear to bethe most obvious candidates for nonradiative defects, and we thus compare theexciton decay times measured for a variety of GaN nanowire ensembles withdifferent surface-to-volume ratio and coalescence degrees. The data are foundto exhibit no correlation with either of these parameters, i. e., thedominating nonradiative channel in the GaN nanowires under investigation isneither related to the nanowire surface, nor to coalescence-induced defects forthe present samples. Hence, we conclude that nonradiative point defects are theorigin of the fast recombination dynamics of excitons in GaN nanowires.

Investigating the origin of the nonradiative decay of bound excitons in GaN nanowires