Enhanced Trion Emission and Carrier Dynamics in Monolayer WS₂ Coupled with Plasmonic Nanocavity

Abstract In 2D transition metal dichalcogenides (TMDs), trions have important applications in fundamental studies of multibody phenomena, novel optoelectronic devices, and valleytronic devices. However, the enhancement of trion emission, and in particular how the carrier dynamics is influenced when coupled with plasmonic cavity, is important for a deep understanding of trions and their further utilization. In this study, strong trion emission is achieved by coupling monolayer WS₂ with a plasmonic nanocavity. Temperature‐dependent photoluminescence, dark‐field scattering measurement, and transient absorption spectroscopy are employed to investigate the trion and exciton behaviors in the hybrid structure. In plasmonic nanocavity, trion emission is enhanced by an order of magnitude, which is attributed to the conversion of excitons to trions via capturing photoionized carriers facilitated by Fano resonance. Further, the ultrafast dynamics of trions and excitons suggest that the plasmonic nanocavity enhances the hole cooling process and radiative recombination of excitons, as well as the formation and recovery process of trions. The results not only explain the enhancement of trion emission and carrier dynamics in the hybrid system but also provide one feasible method to obtain strong trion emission in TMDs, which makes the hybrid system a promising candidate for optoelectronic and valleytronic applications.