Ultrathin lateral 2D photodetectors using transition-metal dichalcogenides PtSe₂–WS₂–PtSe₂ by direct laser patterning

Layer-dependent band structure evolution of transition-metal dichalcogenides (TMDs) endows them with various bandgaps from insulating to semiconducting to conductive. Here, we demonstrate a metal–semiconductor–metal (MSM) photodetector using only TMD materials for both electrodes and photoactive materials. Semimetal few-layered PtSe2 acts as metal electrodes, and monolayer WS2 acts as a photoactive material. PtSe2 was synthesized by thermally assisted selenization, and the device was fabricated by using photolithography coupled with direct laser patterning. By modifying the scanning step during the laser patterning process, various channel widths can be achieved. As-fabricated devices exhibit a satisfactory ON/OFF ratio and fair photoresponse. A comparison study shows that a device with a shorter channel width has better photoresponsivity. A back-to-back Schottky diode model estimates well the barrier height of the PtSe2/WS2 heterojunction. The device also exhibits the lowering of barrier height with increasing laser power, owing to the photogating effect. Our study widens the material choices for 2D electrodes and investigates the feasibility of the low-cost laser patterning on the fabrication of optoelectronic devices.