Strain Control of the Exciton Dynamics in WS2 Monolayers

Two-dimensional transition-metal dichalcogenides blend attractive semiconducting electronic properties with remarkable light–matter interaction. Their optoelectronic, photonic, and light-harvesting functionalities are determined by the nonequilibrium behavior of photogenerated charges and excitons, whose resonant energy, effective mass, and mobility depend crucially on the strain applied to the lattice. Nevertheless, very few studies have directly assessed the role of strain in controlling the most relevant photophysical processes occurring on the femto- and picosecond time scales. Here, we report the modulation of the exciton recombination in monolayer WS2 via the application of uniaxial tensile strain. For 1% applied strain the dominant (few-ps) recombination time decreases over the unstrained case by a factor of 2. We ascribe these fast dynamics to the exciton migration toward ultrafast recombination centers and the strain-induced enhancement of this process to an increased exciton diffusion. This trend is confirmed by a corresponding decrease in the calculated electron and hole effective masses for a strained lattice. Such control over the exciton lifetime suggests that strain can play a crucial role in enhancing luminescent and lasing applications as well as for encoding information in excitons.