Charge-Accumulation Effect in Transition Metal Dichalcogenide Heterobilayers.

Charge transfer in transition-metal-dichalcogenides (TMDs) heterostructures is a prerequisite for the formation of interlayer excitons, which hold great promise for optoelectronics and valleytronics. Charge accumulation accompanied by a charge-transfer process can introduce considerable effect on interlayer exciton-based applications; nevertheless, this aspect has been rarely studied up to date. This work demonstrates how the charge accumulation affects the light emission of interlayer excitons in van der Waals heterobilayers (HBs) consisting of monolayer WSe2 and WS2. As excitation power increases, the photoluminescence intensity of interlayer excitons increases more rapidly than that of intralayer excitons. The phenomenon can be explained by charge-accumulation effect, which not only increases the recombination probability of interlayer excitons but also saturates the charge-transfer process. This scenario is further confirmed by a careful examination of trion binding energy of WS2, which nonlinearly increases with the increase of the excitation power before reaching a maximum of about 75 meV. These investigations provide a better understanding of interlayer excitons and trions in HBs, which may provoke further explorations of excitonic physics as well as TMDs-based devices.