Two-dimensional (2D) transition metal dichalcogenide (TMDC) materials such as MoS2, WS2, MoSe2, and WSe2 have recently emerged as a topical area of physical science and engineering. It has been widely believe that one of the most appealing applications of these materials is in photonics due to their semiconducting nature, perfect surface passivation, and extraordinarily strong exciton binding energies. These materials promise to open up a new age of atomic-scale photonics in which the devices would be scaled a truly atomic level to provide high performance and exotic functionalities. However, the understanding for the fundamental photophysics of 2D TMDC materials has remained limited, which stands as a major challenge for the development of the atomic-scale devices.
In this talk, I will present the recent progress that my group has obtained in understanding the light-matter interactions and exciton dynamics of 2D TMDC materials, in particular, MoS2 and WS2. Many of the results are unexpected and cannot find analog in conventional semiconductor materials. We find that the dielectric function of atomically thin MoS2 films is dominated by excitonic effects. This is in stark contrast from the conventional semiconductor materials, whose dielectric functions are usually dominated by the effect of band structures. We have also demonstrated that 2D heterostructures and substrates can provide sophisticated ways to engineer the exicton dynamics in 2D TMDC materials. By leveraging on the new fundamental understanding, we have developed a variety of novel photonic devices such as atomically thin superabsorbers (absorption efficiency > 70%) for narrowband and broadband (bandwidth > 300 nm) incident light. Our results have clearly indicate the promise of 2D TMDC materials for the next-generation photonic devices, including solar cells, lasers, LEDs, photodetectors, modulators, and photocatalysts.