Spatiotemporal Microwave Imaging of Photo-carrier Dynamics in Monolayer Semiconductors

The spatiotemporal evolution of photo-generated charge carriers in two-dimensional transition-metal dichalcogenides (TMDs) plays a crucial role for their optoelectronic applications. A comprehensive understanding of such dynamics, however, remains a challenging task. Here, we report the simultaneous spatial and temporal photoconductivity imaging in WS₂ monolayers by laser-illuminated microwave impedance microscopy. The diffusion length and carrier lifetime were directly measured. Time-resolved experiments indicate that the critical process for photo-carriers is the escape of holes from defect-induced trap states, which prolong the apparent lifetime of mobile electrons in the conduction band. This work provides fundamental knowledge on the defect-mediated spatiotemporal dynamics of charge carriers in 2D TMDs, paving the way for their applications in novel optoelectronic devices.