Novel Optical and Electrical Transport Properties in Atomically Thin WSe₂/MoS₂ p–n Heterostructures

Vertically stacked Van der Waals heterojunctions of atomically thin transition metal dichalcogenides (TMDs) offer new physical properties and new strategies for designing novel device functionalities that are vastly different from homostructured TMDs. The Raman intensity is strongest and frequency difference is largest in monolayer WSe₂ compared with that in few-layers, which is opposite to MoS₂ and WS₂. In the WSe₂/MoS₂ bilayer heterostructures, inefficient charge transfer quenches light emission of monolayer WSe₂ but strengthens those of MoS₂ monolayer. Interestingly, rectification and ambipolar effects emerge due to tunneling-assisted interlayer recombination and dual conducting channels of p-WSe₂ and n-MoS₂ in the heterojunctions system. Gate-induced holes tunneling also leads to a novel “anti-bipolar” behavior with a sharp current peak. Under light illumination, charge transfer competes with the holes tunneling between the WSe₂ and MoS₂ layers, which can greatly influence the electrical transport leading to the disappeared rectifying and “anti-bipolar” properties.