▎ 摘　　要

Two-dimensional (2D) tungsten disulfide (WS2) became fascinating for optoelectronic applications due to its direct bandgap, high carrier mobility, chemical stability, and strong light-matter interactions. The comple-mentary properties of van der Waals (vdW) heterostructures of 2D WS2 with graphene promise excitonic op-toelectronic performance; however, the strong recombination of excitons in WS2 is a challenge for obtaining a sensitive photodetector. In this work, the effect of geometry and graphene contact on photosensitivity was studied. WS2 nanosheets were prepared by chemical vapor deposition on Si/SiO2 wafers through sulfurization of WO3 at 830 ???C. Atomic force microscopy determined the triangular shape and ???1 nm thick nanosheets with ~20 ??m lateral sizes. Graphene nanosheets with ???100 ??m lateral dimensions were prepared by the scotch-tape method. Raman spectroscopy determined that the graphene was mostly mono-layered with minimum defects (I2D/IG = 2.5). Devices composed of vdW heterostructures showed a photoresponsivity of 198 mAW-1, detec-tivity of 9.2*108 Jones at 535 nm, and a power density of 1.97 mW/cm2. However, slightly inferior responses were detected in the range of visible wavelengths. The results are discussed based on the electronic band alignment of the heterostructure. Our finding may pave the way toward high-performance flexible broadband optoelectronic devices based on engineering vdW two-dimensional materials.