Exciton tuning in monolayer WSe${}_2$ via substrate induced electron doping

Abstract

We report on large exciton tuning in WSe${}_2$ monolayers via substrate induced non-degenerate doping. We observe a redshift of $\sim$62 meV for the $A$ exciton together with a 1-2 orders of magnitude photoluminescence (PL) quenching when the monolayer WSe${}_2$ is brought in contact with highly oriented pyrolytic graphite (HOPG) compared to the dielectric substrates such as hBN and SiO${}_2$. As the evidence of doping from HOPG to WSe${}_2$, a drastic increase of the trion emission intensity was observed. Using a systematic PL and Kelvin probe force microscopy (KPFM) investigation on WSe${}_2$/HOPG, WSe${}_2$/hBN, and WSe${}_2$/graphene, we conclude that this unique excitonic behavior is induced by electron doping from the substrate. Our results propose a simple yet efficient way for exciton tuning in monolayer WSe${}_2$, which plays a central role in the fundamental understanding and further device development.

14 pages, 10 figures