Neutral and charged dark excitons in monolayer WS$_2$

TL;DR

This study uses magneto-photoluminescence to analyze dark excitons and trions in monolayer WS$_2$, revealing their properties, interactions, and magnetic responses, with implications for 2D semiconductor optoelectronics.

Contribution

It provides the first detailed characterization of dark trions in monolayer WS$_2$, including their g-factor, decay rate, and polarization properties, expanding understanding of dark excitonic states.

Findings

Dark trions dominate the emission spectrum.

Dark trions have a g-factor of approximately -8.6.

Dark trions exhibit a decay time of about 0.5 ns.

Abstract

Low temperature and polarization resolved magneto-photoluminescence experiments are used to investigate the properties of dark excitons and dark trions in a monolayer of WS$_2$ encapsulated in hexagonal BN (hBN). We find that this system is an $n$-type doped semiconductor and that dark trions dominate the emission spectrum. In line with previous studies on WSe$_2$, we identify the Coulomb exchange interaction coupled neutral dark and grey excitons through their polarization properties, while an analogous effect is not observed for dark trions. Applying the magnetic field in both perpendicular and parallel configurations with respect to the monolayer plane, we determine the g-factor of dark trions to be $g\sim$-8.6. Their decay rate is close to 0.5 ns, more than 2 orders of magnitude longer than that of bright excitons.