Role of defects in the photoluminescence and photoresponse of WS2–graphene heterodevices

[Display omitted] •A new CVD process is proposed, and the number of sulfur vacancies in monolayer WS2 flakes is well controlled.•By characterizing the photoluminescence intensity, it is easy to select WS2 flakes with different densities of sulfur vacancies.•Scanning transmission electron microscopy images and the photoresponse exhibited the predicted tendency. Two-dimensional (2D) transition metal dichalcogenides are promising materials for next-generation photodetectors. Therefore, controlling point chalcogen vacancies in chemical vapor deposition (CVD) synthesis is inevitable. In this work, the number of sulfur vacancies in monolayer WS2 flakes is well controlled in CVD synthesis, which resulted in a photoluminescence (PL) intensity difference. In addition, the relationship between the PL intensity and photoresponse of monolayer WS2 on graphene is discussed. The sulfur vacancies introduce defect trap states that cause carrier recombination and reduce carrier drift to graphene, thus decreasing the photocurrent. Furthermore, the gate-tunable Fermi level of graphene allows tunable responsivity of the WS2–graphene photodetector of up to 5 A/W with metal hard-mask fabrication. Our findings on the PL intensity and responsivity provide a simple and efficient strategy for choosing high-performance CVD-synthesized 2D TMD photodetectors.