Dark trions govern the temperature-dependent optical absorption and emission of doped atomically thin semiconductors
Ashish Arora, Nils Kolja Wessling, Thorsten Deilmann, Till Reichenauer, Paul Steeger, P. Kossacki, M. Potemski, Steffen Michaelis de Vasconcellos, Michael Rohlfing, Rudolf Bratschitsch
Abstract
We perform absorption and photoluminescence spectroscopy of trions in hBN-encapsulated $\mathrm{WS}{\mathrm{e}}_{2}$, ${\mathrm{WS}}_{2},\phantom{\rule{0.28em}{0ex}}\mathrm{MoS}{\mathrm{e}}_{2}$, and $\mathrm{Mo}{\mathrm{S}}_{2}$ 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, ${X}_{\mathrm{D}}^{\ensuremath{-}}$, 19 meV below the lowest bright trion, ${X}_{1}^{\ensuremath{-}}$, in $\mathrm{WS}{\mathrm{e}}_{2}$ and $\mathrm{W}{\mathrm{S}}_{2}$. In $\mathrm{MoS}{\mathrm{e}}_{2}$, ${X}_{\mathrm{D}}^{\ensuremath{-}}$ lies 6 meV above ${X}_{1}^{\ensuremath{-}}$, while ${X}_{\mathrm{D}}^{\ensuremath{-}}$ and ${X}_{1}^{\ensuremath{-}}$ almost coincide in $\mathrm{Mo}{\mathrm{S}}_{2}$. Our results agree with GW-Bethe-Salpeter equation (GW-BSE) ab initio calculations and quantitatively explain the optical response of doped monolayers with temperature.