Dark trions govern the temperature-dependent optical absorption and emission of doped atomically thin semiconductors

TL;DR

This study investigates how dark and bright trions influence the temperature-dependent optical properties of doped monolayer semiconductors, revealing material-specific energy orderings and confirming findings with ab-initio calculations.

Contribution

It provides a comprehensive experimental and theoretical analysis of dark and bright trions in various doped monolayer semiconductors, highlighting their energy relationships and temperature effects.

Findings

Dark trion $ m{X_D^-}$ is below bright trion in WSe$_2$ and WS$_2$.

In MoSe$_2$, dark trion is above the bright trion.

Results align with GW-BSE ab-initio calculations.

Abstract

We perform absorption and photoluminescence spectroscopy of trions in hBN-encapsulated WSe$_2$, WS$_2$, MoSe$_2$, and MoS$_2$ monolayers, depending on temperature. The different trends for W- and Mo-based materials are excellently reproduced considering a Fermi-Dirac distribution of bright and dark trions. We find a dark trion, $\rm{X_D^-}$ 19 meV $\textit{below}$ the lowest bright trion, $\rm{X}_1^-$ in WSe$_2$ and WS$_2$. In MoSe$_2$, $\rm{X_D^-}$ lies 6 meV $\textit{above}$ $\rm{X}_1^-$, while $\rm{X_D^-}$ and $\rm{X}_1^-$ almost coincide in MoS$_2$. Our results agree with GW-BSE $\textit{ab-initio}$ calculations and quantitatively explain the optical response of doped monolayers with temperature.