Lateral Graphene-Contacted Vertically Stacked WS₂ /MoS₂ Hybrid Photodetectors with Large Gain

A demonstration is presented of how significant improvements in all-2D photodetectors can be achieved by exploiting the type-II band alignment of vertically stacked WS₂ /MoS₂ semiconducting heterobilayers and finite density of states of graphene electrodes. The photoresponsivity of WS₂ /MoS₂ heterobilayer devices is increased by more than an order of magnitude compared to homobilayer devices and two orders of magnitude compared to monolayer devices of WS₂ and MoS₂ , reaching 10³ A W^-1 under an illumination power density of 1.7 × 10² mW cm^-2 . The massive improvement in performance is due to the strong Coulomb interaction between WS₂ and MoS₂ layers. The efficient charge transfer at the WS₂ /MoS₂ heterointerface and long trapping time of photogenerated charges contribute to the observed large photoconductive gain of ≈3 × 10⁴ . Laterally spaced graphene electrodes with vertically stacked 2D van der Waals heterostructures are employed for making high-performing ultrathin photodetectors.