Layer-dependent excitonic valley polarization properties in MoS2-WS2 heterostructures

Layered transition metal dichalcogenides (TMDCs) pave the way for fundamental research on atomically thin materials and optoelectronic devices. Due to their intrinsic 2D nature, few-layer TMDCs heterostructures exhibit several unique physical properties that are extremely sensitive to the number of layers. However, studies on the effects of interlayer coupling on excitons and valley polarization are still insufficient. Here, we investigate the polarization of the excitonics valley in MoS2-WS2 heterostructures using circular polarization-resolved photoluminescence. The valley polarization is the largest (~28.45%) in 1L-1L MoS2-WS2 heterostructure and the polarizability of the A_(〖WS〗_2 ) decreases as the number of WS2 layers increases. The layer-dependent valley polarization can be explained by the indirect bandgap nature of multilayer WS2. We further observed a red shift of exciton X_(〖MoS〗_2)^- in MoS2-WS2 heterostructures with the increase of WS2 layers, which is attributed to the displacement of MoS2 band edge, indicating the layer sensitive optical properties of MoS2-WS2 heterostructure. Our findings shed light on the understanding of exciton behavior in multilayer MoS2-WS2 heterostructures that may promote their potential applications in optoelectronic devices.