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

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.