Transport Dynamics of Neutral Excitons and Trions in Monolayer WS2

Understanding the spatial motion of excitons is of both fundamental interest and central importance for optoelectrical applications. Here, we have investigated the temperature (T) dependence of the transport dynamics of neutral excitons and charged excitons (trions) in atomically thin two-dimensional crystals of the transition-metal dichalcogenide WS2. The transport dynamics of neutral excitons can be divided into three temperature ranges, where the diffusion of neutral excitons is governed by thermal activation (<=similar to 75 K), ionized impurity scattering (similar to 75 K <= T <=similar to 200 K), and LO phonon scattering (>=similar to 200 K). The trions have a diffusion length that is over 20 times longer than that of neutral excitons at very low temperatures (<=similar to 10 K), which may be related to theoretically predicted Pauli-blocking effects during the excitation process.