Synergistic effect of polymer encapsulated silver nanoparticle doped WS sheets for plasmon enhanced 2D/3D heterojunction photodetectors.

Chemical doping and plasmonic enhanced photoresponsivity of two dimensional (2D) n-WS/p-Si heterojunctions are demonstrated for the first time. Novel PVP coated Ag intercalation induced synthesis has led to the formation of impurity-free, chemically doped few-layer n-WS with reversed conductivity following the Maxwell-Wagner-Sillars interfacial effect. The resultant composite film exhibits excellent stability and tunable plasmonic absorption due to silver nanoparticles of different sizes. A sharp band-edge absorption of the hybrid material indicates the presence of spin-orbit coupled direct band gap transitions in WS layers, in addition to a broader plasmonic peak attributed to Ag nanoparticles. Stabilized Ag-nanoparticle (∼4-6 nm) embedded electron rich n-WS has been used to fabricate plasmon enhanced, silicon compatible heterojunction photodetectors. The detectors exhibited superior properties, possessing a photo-to-dark current ratio of ∼10, a very high responsivity (8.0 A W) and an EQE of 2000% under 10 V bias with a broad spectral photoresponse in the wavelength range of 400-1100 nm. The results provide a new paradigm for intercalant impurity-free metal nanoparticle assisted exfoliation of n-type few-layer WS, with the nanoparticles playing a dual role towards the realization of 2D materials based broadband heterojunction optoelectronic devices by inducing chemical doping as well as tunable plasmon enhanced absorption.