Efficient Optical Modulation of Exciton State Population in Monolayer MoS(2) at Room Temperature

The modulation of exciton energy and state density of layer-structured transition metal dichalcogenides (TMDs) is required for diverse optoelectronic device applications. Here, the spontaneous inversion of exciton state population in monolayer MoS(2) is observed by turning the pump light power. The excitons prefer to exist in low energy state under low pump power, but reverse under high pump power. To discuss the mechanism in depth, we propose a semiclassical model by combining the rate equation and photo−exciton interaction. Considering the modifying of exciton−exciton annihilation, the spontaneous inversion of exciton state population is phenomenologically described.