Anomalously polarised emission from a MoS(2)/WS(2) 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.