On-chip manipulation of trion drift in suspended WS2 monolayer at room temperature

Excitons, which are bound states of electrons and holes, in transition metal dichalcogenides (TMDCs) have been studied as an information carrier for realizing new types of optoelectronic devices. However, the charge neutrality of excitons inhibits the electric control of their motion, as seen in conventional electronic devices, except when utilizing a heterostructure. Here, we investigated the drift motion of trions, quasiparticles composed of an exciton bound to an excess charge, at room temperature in a suspended WS2 monolayer by applying a gate-tunable electric field. Using a simple bottom-gate device, we can tune the electric field intensity and exciton-to-trion conversion ratio by increasing the charge density in the monolayer. Consequently, we experimentally observed that locally excited trions drift toward the center of the suspended monolayer. To understand the underlying mechanisms, we numerically simulated the trion drift using the drift-diffusion equation, accounting for the contributions from both the electric field and strain. The results confirmed that the electric field plays the dominant role in the drift phenomena. Our work offers a useful platform for realizing trion-based optoelectronic devices that are capable of operating even at room temperature.