The influence of the environment on monolayer tungsten diselenide photoluminescence

Abstract We report on a comprehensive experimental analysis of the influence of the environment on the optical properties of monolayer WSe 2 . Different dielectric-environmental configurations with hBN as buffer and encapsulant were studied at room temperature and 10 K using time-integrated and time-resolved photoluminescence spectroscopy. Furthermore, Raman signal was evaluated to highlight the influence of the surroundings on the monolayer system. Here, linewidth and intensity improvement for 2D excitons as a consequence of hBN-encapsulation is demonstrated, and a change of strain and doping levels in our produced structures are observed. The increase of the exciton radius for hBN-buffered samples in comparison to WSe 2 on bare substrates is indicated via an exciton–exciton annihilation study, while hBN as buffer is found to generally shorten the effective radiative lifetime. Furthermore, we report that trions experience a weaker interaction with the WSe 2 phonons than excitons, while the coupling to phonons is consistently decreased when WSe 2 is capped by hBN. Ultimately, our energy-resolved analysis of the dynamics at 10 K shows that the individual excitonic modes exhibit different photoluminescence decay times. A comparison of the different hBN-WSe 2 configurations shows that the shortest measurable time constants, which are on the ps-scale, generally increase when buffering or encapsulating the 2D semiconductor, while sandwiching caused the strongest lifetime increase on these short time scales. In contrast, our monolayer–monolayer heterostructures indicate fast charge/energy transfer ( 2 to WSe 2 and a comparably slow radiative recombination of the type-I A excitons depending on the tilt angle between the two lattices.