Ultrafast Dynamics of Defect-Assisted Electron-Hole Recombination in Monolayer MoS2

TL;DR

This study investigates ultrafast electron-hole recombination in monolayer MoS2, revealing defect-assisted Auger processes as the dominant mechanism with two distinct recombination timescales, supported by experimental data and theoretical modeling.

Contribution

It provides the first detailed ultrafast optical measurements and a quantitative model demonstrating defect-assisted Auger recombination as the key process in monolayer MoS2.

Findings

Recombination occurs on two timescales: ~2 ps and >100 ps.

Defect-assisted Auger processes dominate electron-hole recombination.

Model estimates align with experimental rate constants.

Abstract

In this letter, we present non-degenerate ultrafast optical pump-probe studies of the carrier recombination dynamics in MoS$_{2}$ monolayers. By tuning the probe to wavelengths much longer than the exciton line, we make the probe transmission sensitive to the total population of photoexcited electrons and holes. Our measurement reveals two distinct time scales over which the photoexcited electrons and holes recombine; a fast time scale that lasts $\sim$2 ps and a slow time scale that lasts longer than $\sim$100 ps. The temperature and the pump fluence dependence of the observed carrier dynamics are consistent with defect-assisted recombination as being the dominant mechanism for electron-hole recombination in which the electrons and holes are captured by defects via Auger processes. Strong Coulomb interactions in two dimensional atomic materials, together with strong electron and hole correlations in two dimensional metal dichalcogenides, make Auger processes particularly effective for carrier capture by defects. We present a model for carrier recombination dynamics that quantitatively explains all features of our data for different temperatures and pump fluences. The theoretical estimates for the rate constants for Auger carrier capture are in good agreement with the experimentally determined values. Our results underscore the important role played by Auger processes in two dimensional atomic materials.