Radiative and nonradiative decay of excitons in GaN nanowires

Abstract

GaN nanowires form spontaneously on a wide variety of substrates without suffering from extended defects. However, their quasi-one-dimensional nature causes these structures to have an extended free surface, resulting in a surface-to-volume ratio orders of magnitude larger than that of a planar layer. Additionally, the high nucleation density of spontaneously formed GaN nanowire ensembles results in an unintentional, but inevitable coalescence between individual nanowires. In this work, we investigate the impact of both the surface and the coalescence of nanowires on the recombination dynamics of excitons in GaN nanowire ensembles. Using simple models to simulate the change in recombination dynamics of bound excitons in GaN NWs with varying diameter and coalescence degree, we show that the comparatively short decay times at low temperatures are not generally caused by either of these mechanisms. Furthermore, we demonstrate that the biexponential decay for the donor-bound exciton is also not related to a coexistence of nonradiative and radiative recombination channels, but originates from a coupling of the donor- and acceptor-bound exciton states in the GaN NWs.