Carrier and polarization dynamics in monolayer MoS2

TL;DR

This study investigates the polarization and exciton dynamics in monolayer MoS2, revealing temperature-independent polarization properties, ultrafast decay times, and the influence of excitation power and photon energy on emission polarization.

Contribution

It provides new insights into the polarization stability and ultrafast exciton decay in monolayer MoS2 across a wide temperature range.

Findings

High polarization maintained from 4K to 300K.

Ultrafast exciton decay time of about 4ps.

Emission polarization decreases with increasing laser power.

Abstract

In monolayer MoS2 optical transitions across the direct bandgap are governed by chiral selection rules, allowing optical valley initialization. In time resolved photoluminescence (PL) experiments we find that both the polarization and emission dynamics do not change from 4K to 300K within our time resolution. We measure a high polarization and show that under pulsed excitation the emission polarization significantly decreases with increasing laser power. We find a fast exciton emission decay time on the order of 4ps. The absence of a clear PL polarization decay within our time resolution suggests that the initially injected polarization dominates the steady state PL polarization. The observed decrease of the initial polarization with increasing pump photon energy hints at a possible ultrafast intervalley relaxation beyond the experimental ps time resolution. By compensating the temperature induced change in bandgap energy with the excitation laser energy an emission polarization of 40% is recovered at 300K, close to the maximum emission polarization for this sample at 4K.