Revealing Excitonic Complexes in Monolayer WSe2

Single layer transition metal dichalcogenides (TMDs) represent a new class of atomically thin semiconductors with superior optical and optoelectronic properties. The two-dimensional nature of single-layer TMDs results in reduced screening and enhanced Coulomb interaction, giving rise to excitonic complexes such as exciton, trion, and biexciton with binding energy orders of magnitude larger than that of conventional semiconductors such as GaAs. The excitonic complexes also possess valley degree of freedom and can be accessed selectively through circularly polarized light. Here we show that by encapsulating the monolayer WSe2 with BN, we can construct devices with high-quality optical spectra which helps to identify fine features of excitonic complexes. The BN encapsulated monolayer WSe2 thus provides an exciting playground for the strong light-matter interaction in 2D.