Anomalously polarised emission from a MoS2/WS2 heterostructure

We report circularly polarised emission, with helicity opposite to the optical excitation, from a van der Waals heterostructure (HS) consisting of a monolayer MoS 2 and three-layer WS 2 . Selective excitation of the MoS 2 layer confirms that this cross-polarized emission is due to the charge transfer from the WS 2 layers to the MoS 2 layer. We propose that the high levels of n-doping in the constituent layers due to sulphur vacancies and defects give rise to an enhanced transition rate of electrons from the k valley of WS 2 to the k ′ valley of MoS 2 , which leads to the emission, counter polarized to the excitation. Simulations based on the rate equation model support this conclusion. The brightening of a dark exciton state in the MoS 2 layer due to doping and charge transfer from WS 2 to this dark state gives rise to circularly polarized emission, from a MoS 2 /WS 2 heterostructure, with helicity opposite to that of the excitation.