High-Performance Planar Field-Emission Photodetector of Monolayer Tungsten Disulfide with Microtips.

ABSTRACT

Monolayer tungsten disulfide (ML WS2 ) is believed as an ideal photosensitive material due to its small direct bandgap, large exciton/trion binding energy, high carrier mobility, and considerable quantum conversion efficiency. Compared with other photosensitive devices, planar field emission (FE)-type photodetectors with a full-plane structure should simultaneously have rapider switching speed and lower power consumption. In this work, ML WS2 microtips are fabricated by electron beam lithography (EBL) way and used to construct a planar FE-type photodetector. By optimization design, ML WS2 with three microtips can exhibit the maximum current density as high as  52 A cm-2 (@300 V µm-1 ), and the largest photoresponsivity is up to 6.8 × 105 A W-1 under green light irradiation, superior to that of many other ML transition metal dichalcogenide (TMDC) detectors. More interestingly, ML WS2 devices with microtips can effectively solve the contradictory problem between large photoresponsivity and rapid switching speed. The excellent photoresponse performances of ML WS2 with microtips should be attributed to their high carrier mobility, sharp emission edge, ultrahigh quantum yield, and unique planar FE device structure. Our research may shed new light on exploring the fabrication technology and photosensitive mechanism of two dimensional (2D) material-based planar FE photodetectors.