Manipulation of exciton dynamics is a fundamental approach for exploiting the valley degree of freedom in two-dimensional van der Waals (vdWs) heterostructures and developing high-performance valleytronic devices. Herein, we report a method for controlling interlayer spin-charge transfer in WS₂/CrBr₃ vdWs heterostructure through graphene proximity coupling and achieve a giant chirality-dependent valley polarization splitting. Theoretical and experimental findings reveal that the WS₂/CrBr₃ vdWs heterostructure retains its initial large conduction band offset under light irradiation when it is coupled with a few-layered graphene in the bottom. The interlayer spin-charge transfer time is significantly reduced from 17.3 ps to 1.3 ps, leading to a remarkable improvement in the valley polarization. The degree of valley polarization and polarization splitting of trion excitons in WS₂ are enhanced by 32% and 261%, respectively. Moreover, a highly sensitive circularly polarized photodetector was developed by using the WS₂/CrBr₃/graphene heterostructure. This work pioneers a route to efficiently manipulate the transport behavior of excitons in vdWs heterostructures and also offers a novel idea for designing high-performance spintronic devices.

Vertical van der Waals (vdW) heterostructures composed of two-dimensional (2D) layered materials have recently attracted substantial interests due to their unique properties. However, the direct synthesis of moiré superlattice remains a great challenge due to the difficulties in heterogeneous nucleation on smooth vdW surfaces. Here, we report a controllable chemical vapor deposition growth of complete monolayer WS₂ on highly ordered pyrolytic graphite (HOPG) substrates through the plasma pretreatment. The results show that the morphologies of the grown WS₂ have a strong dependence on the plasma parameters, including gas composition, source power, and treatment time. It is found that the surface C–C bonds are broken in the plasma pretreated HOPG, and the formed small clusters can act as the nucleation sites for the subsequent growth of WS₂. Moreover, the height of clusters dominates the growth mode of WS₂ islands. A transition from a 2D mode to three-dimensional (3D) growth mode occurs when the height is higher than the interlayer spacing of the heterostructure. Besides, diverse moiré superlattices with different twist angles for WS₂/HOPG heterostructures are observed, and the formation mechanism is further analyzed by first-principles calculations.