Anomalously polarised emission from a MoS2/WS2heterostructure

Abstract

We report circularly polarised emission, with helicity opposite to the optical excitation, from a van der Waals heterostructure (HS) consisting of a monolayer MoS2 and three-layer WS2. Selective excitation of the MoS2 layer confirms that this cross-polarized emission is due to the charge transfer from the WS2 layers to the MoS2 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 WS2 to the k′ valley of MoS2, which leads to the emission, counter polarized to the excitation. Simulations based on the rate equation model support this conclusion.