Coupling of exciton states as the origin of their biexponential decay dynamics in GaN nanowires

TL;DR

This paper investigates the biexponential decay of excitons in GaN nanowires, revealing that strong coupling between exciton states causes this behavior, as shown through spectroscopy and modeling.

Contribution

It demonstrates that exciton coupling, not surface effects, causes biexponential decay in GaN nanowires, supported by experimental data and rate-equation modeling.

Findings

Biexponential decay is not due to surface effects.

Strong coupling between exciton states causes decay dynamics.

Model reproduces experimental decay behavior.

Abstract

Using time-resolved photoluminescence spectroscopy, we explore the transient behavior of bound and free excitons in GaN nanowire ensembles. We investigate samples with distinct diameter distributions and show that the pronounced biexponential decay of the donor-bound exciton observed in each case is not caused by the nanowire surface. At long times, the individual exciton transitions decay with a common lifetime, which suggests a strong coupling between the corresponding exciton states. A system of non-linear rate-equations taking into account this coupling directly reproduces the experimentally observed biexponential decay.