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

TL;DR

This study investigates the rapid nonradiative recombination of excitons in GaN nanowires, revealing that point defects, rather than surface or coalescence defects, dominate the decay process across a range of temperatures.

Contribution

It demonstrates that nonradiative decay in GaN nanowires is primarily caused by point defects, challenging previous assumptions about surface or coalescence-related defects being the main factors.

Findings

Nonradiative decay dominates between 10 and 300 K.

Bound and free excitons are strongly coupled with a common lifetime.

Decay times do not correlate with surface-to-volume ratio or coalescence degree.

Abstract

We investigate the origin of the fast recombination dynamics of bound and free excitons in GaN nanowire ensembles by temperature-dependent photoluminescence spectroscopy using both continuous-wave and pulsed excitation. The exciton recombination in the present GaN nanowires is dominated by a nonradiative channel between 10 and 300 K. Furthermore, bound and free excitons in GaN NWs are strongly coupled even at low temperatures resulting in a common lifetime of these states. By solving the rate equations for a coupled two-level system, we show that one cannot, in practice, distinguish whether the nonradiative decay occurs directly via the bound or indirectly via the free state. The nanowire surface and coalescence-induced dislocations appear to be the most obvious candidates for nonradiative defects, and we thus compare the exciton decay times measured for a variety of GaN nanowire ensembles with different surface-to-volume ratio and coalescence degrees. The data are found to exhibit no correlation with either of these parameters, i. e., the dominating nonradiative channel in the GaN nanowires under investigation is neither related to the nanowire surface, nor to coalescence-induced defects for the present samples. Hence, we conclude that nonradiative point defects are the origin of the fast recombination dynamics of excitons in GaN nanowires.