Exciton tuning in monolayer WSe substrate induced electron doping.

We report large exciton tuning in WSe monolayers 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 is brought in contact with highly oriented pyrolytic graphite (HOPG) compared to dielectric substrates such as hBN and SiO. As the evidence of doping from HOPG to WSe, a drastic increase of the intensity ratio of trions to neutral excitons was observed.