Radiative lifetime of localized excitons in transition metal dichalcogenides

TL;DR

This paper models disorder-induced localized excitons in monolayer WSe2, revealing how defect-related potential variations extend radiative lifetimes and influence optical properties, validated against experimental data.

Contribution

It introduces a randomized potential model to simulate localized exciton spectra and lifetimes in monolayer TMDs, linking disorder parameters to optical behavior.

Findings

Localized excitons have longer emission times than free excitons.

Radiative lifetime depends strongly on disorder and dielectric environment.

Model predictions agree with experimental results.

Abstract

Disorder derived from defects or strain in monolayer TMDs can lead to a dramatic change in the physical behavior of the interband excitations, producing inhomogeneous spectral broadening and localization; leading to radiative lifetime increase. In this study, we have modeled the disorder in the surface of the sample through a randomized potential in monolayer WSe2. We show that this model allows us to simulate the spectra of localized exciton states as well as their radiative lifetime. In this context, we give an in depth study of the influence of the disorder potential parameters on the optical properties of these defects through energies, density of states, oscillator strengths, photoluminescence (PL) spectroscopy and radiative lifetime at low temperature (4K). We demonstrate that localized excitons have a longer emission time than free excitons, in the range of tens of picoseconds or more, and we show that it depends strongly on the disorder parameter and dielectric environment. Finally, in order to prove the validity of our model we compare it to available experimental results of the literature.