# Ga-polar (In,Ga)N/GaN quantum wells vs. N-polar (In,Ga)N quantum disks in GaN nanowires: Comparative analysis of carrier recombination, diffusion, and radiative efficiency

## TL;DR

This study compares carrier recombination, diffusion, and efficiency in Ga-polar (In,Ga)N/GaN quantum wells and N-polar (In,Ga)N quantum disks in GaN nanowires, revealing differences in radiative efficiency and nonradiative decay channels.

## Contribution

It provides a comparative analysis of radiative and nonradiative processes in two different polarities of (In,Ga)N structures, introducing a stochastic model to simulate recombination dynamics.

## Key findings

- Ga-polar quantum wells have two orders of magnitude higher PL intensity than N-polar quantum disks.
- Nonradiative decay channels are highly efficient in quantum disks, reducing their PL intensity.
- Power law decay of recombination persists even with dominant nonradiative processes.

## Abstract

We investigate the radiative and nonradiative recombination processes in planar (In,Ga)N/GaN(0001) quantum wells and (In,Ga)N quantum disks embedded in GaN$(000\bar{1})$ nanowires using photoluminescence spectroscopy under both continuous-wave and pulsed excitation. The photoluminescence intensities of these two samples quench only slightly between 10 and 300 K, which is commonly taken as evidence for high internal quantum efficiencies. However, a side-by-side comparison shows that the absolute intensity of the Ga-polar quantum wells is two orders of magnitude higher than that of the N-polar quantum disks. A similar difference is observed for the initial decay time of photoluminescence transients obtained by time-resolved measurements, indicating the presence of a highly efficient nonradiative decay channel for the quantum disks. In apparent contradiction to this conjecture, the decay of both samples is observed to slow down dramatically after the initial rapid decay. Independent of temperature, the transients approach a power law for longer decay times, reflecting that recombination occurs between individual electrons and holes with varying spatial separation. Employing a coupled system of stochastic integro-differential equations taking into account both radiative and nonradiative Shockley-Read-Hall recombination of spatially separate electrons and holes as well as their diffusion, we obtain simulated transients matching the experimentally obtained ones. The results reveal that even dominant nonradiative recombination conserves the power law decay for (In,Ga)N/GaN{0001} quantum wells and disks.