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

Abstract

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.

WS₂/MoS₂ vertical heterostructures are known to have type-II band alignment and form layer-separated electron–hole pairs upon illumination. Lateral photodetectors based on WS₂/MoS₂ heterostacks with graphene electrodes are demonstrated using crystals grown by chemical vapor deposition. The unique device architecture results in superior photosensing performance with large photoconductive gain due to long-lived interlayer excitons and the photogating mechanism.

http://ift.tt/2hMxiBA