Exciton tuning in monolayer WSe(2)via substrate induced electron doping

We report large exciton tuning in WSe(2) monolayers via substrate induced non-degenerate doping. We observe a redshift of ∼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 dielectric substrates such as hBN and SiO(2). As the evidence of doping from HOPG to WSe(2), a drastic increase of the intensity ratio of trions to neutral excitons 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.