Photoluminescence Saturation and Exciton Decay Dynamics in Transition Metal Dichalcogenide Monolayers

TL;DR

This study compares exciton dynamics and photoluminescence saturation in monolayer MoSe2 and MoS2, revealing significant differences in decay mechanisms, saturation intensities, and exciton lifetimes due to their intrinsic properties.

Contribution

It provides new insights into the distinct exciton decay processes and saturation behaviors in MoSe2 and MoS2 monolayers, highlighting the role of exciton lifetime differences.

Findings

PL saturation occurs at much lower excitation in MoSe2 than MoS2

Nonlinear exciton-exciton annihilation dominates in MoSe2

Exciton lifetime in MoSe2 exceeds 125 ps, much longer than in MoS2

Abstract

We report a photoluminescence (PL) and transient reflection spectroscopy study of exciton dynamics in monolayer transition transition-metal dichalcogenides (TMDs). PL saturation in monolayer MoSe2 occurs an excitation intensity more than two orders of magnitude lower than in monolayer MoS2. Transient reflection shows that the nonlinear exciton-exciton annihilation is the dominant exciton decay process in monolayer MoSe2 in contrast to the previously reported linear exciton decay in monolayer MoS2. In addition, the exciton lifetime in MoSe2, > 125 ps, is more than an order of magnitude longer than the several-ps exciton lifetime in MoS2. We find that the dramatically different exciton decay mechanism and PL saturation behavior of MoSe2 and MoS2 monolayers can be explained by the difference in their exciton lifetime.