Polarization dependent trion dynamics in large area CVD grown 2D monolayer MoS₂ by terahertz time-domain spectroscopy

We investigated the room-temperature transport properties in large area CVD-grown MoS₂ monolayers using terahertz time domain spectroscopy as a function of the intensity and polarization of a continuous wave optical pump at 637 nm. A reduction in conductivity was observed with the generation of photocarriers, which was attributed to generation of trions under optical excitation with both linearly polarized and circularly polarized light. By modifying the Drude conductivity model with inclusion of trions, a dynamic exchange relation between free electrons and generation of trions was established, along with associated carrier concentrations and scattering times, in agreement with experimental observations. Our results provide a better understanding of carrier formation and dynamics during interband transition across the direct gaps at K and K′ points in 2D MoS₂ as a function of optical pump polarization and at room temperature—including quantitatively, which can provide insights toward future developments in MoS₂-based optoelectronics and valleytronic devices. (paper)