Ultrafast Exciton and Charge Carrier Dynamics in Monolayer MoS2 Measured with Time-Resolved Spectroscopic Ellipsometry

Due to their unique optical properties, 2D monolayer transition metal dichalcogenides (TMDCs) show great potential for future electronic and photonic devices, but for real applications, the performance of those is still in need of improvement at the moment. Understanding the exciton and charge carrier dynamics in TMDCs plays a key role in device applications, especially as photonic devices operate under strongly nonequilibrium conditions, as well as for fundamental understanding of the TMDC materials. By employing pump-probe femtosecond time-resolved spectroscopic ellipsometry, the ultrafast exciton/charge carrier dynamics in monolayer MoS2 by studying their impact on the materials dielectric function as a function of time is investigated. From the experiments and analysis of the time-dependent changes in the dielectric function after laser-excitation, a comprehensive model of the dynamics of the excitons, trions, and charge carriers within the Brillouin zone of the electronic structure is derived. The formation of trions, carrier scattering processes between the Gamma- and K-point of the Brillouin zone, arising of new intravalence and intraconduction band transitions, carrier relaxation within the bands, as well as recombination processes are found.