Auger recombination of dark excitons in ${\rm WS_2}$ and ${\rm WSe_2}$ monolayers

TL;DR

This paper identifies a phonon-assisted Auger process that dominates exciton recombination in tungsten-based monolayer TMDCs, explaining their low quantum efficiencies at relatively low carrier densities.

Contribution

It introduces a novel Auger process specific to monolayer TMDCs and combines experimental and DFT calculations to analyze its impact on exciton recombination.

Findings

Auger process dominates at carrier densities of 10^9-10^10 cm^-2

Explains low quantum efficiencies in tungsten-based TMDCs

Provides quantitative analysis using experimental and DFT data

Abstract

We propose a novel phonon assisted Auger process unique to the electronic band structure of monolayer transition metal dichalcogenides (TMDCs), which dominates the radiative recombination of ground state excitons in Tungsten based TMDCs. Using experimental and DFT computed values for the exciton energies, spin-orbit splittings, optical matrix element, and the Auger matrix elements, we find that the Auger process begins to dominate at carrier densities as low as $10^{9-10}~{\rm cm^{-2}}$, thus providing a plausible explanation for the low quantum efficiencies reported for these materials.