A vertically layered MoS2/Si heterojunction for an ultrahigh and ultrafast photoresponse photodetector

Recently, vertically oriented few-layer 2D materials prepared by chemical vapor deposition (CVD) have attracted much attention due to their attractive properties. However, the integration of these materials as heterojunctions in optoelectronic sensors has been rarely reported. In this paper, large-area, high crystalline quality, and vertically oriented few-layered MoS2 (V-MoS2) nanosheets were synthesized and transferred successfully onto a silicon substrate to form a V-MoS2/Si heterojunction photodetector. The photodetector exhibits high photoelectric performances in a wide broadband ranging from visible to near-infrared with a photoresponsivity of up to 908.2 mA W-1, and a detectivity of up to 1.889 x 10(13) Jones. More importantly, an unprecedented response speed of (rise time similar to 56 ns, fall time similar to 825 ns) was found in the photodetector by time response measurements, which is the best result achieved so far in any other 2D-based photodetectors or phototransistors. These excellent performances can be ascribed to the strong light absorption and the quick longitudinal intralayer carrier transport speed of the V-MoS2 nanosheets as well as the good heterojunction formed between V-MoS2 and Si. This intriguing vertical oriented structure in combination with both ultrafast time response and ultrahigh detectivity in the V-MoS2/Si heterojunction provide great potential for application in optoelectronic devices.