Anisotropic exciton drift–diffusion in a monolayer WS_2xSe_(2-2x) alloy with a gradually changing composition

Abstract We demonstrate anisotropic exciton drift–diffusion in a WS2xSe(2-2x) alloy monolayer with a gradually changing exciton energy caused by the spatial variation in the chalcogen composition ratio. The photoluminescence (PL) images under isotropic laser excitation are extended toward the lower exciton energy side. Moreover, the degree of asymmetry in the PL image increases at the positions with a steep exciton energy gradient. The anisotropy in the PL images and its correlation with the exciton energy gradient are reproduced considering the exciton kinetics obeying a drift–diffusion equation. The findings may support the development of excitonic devices using transition metal dichalcogenides.