Self-Driven Metal–Semiconductor–Metal WSe₂ Photodetector with Asymmetric Contact Geometries

Self-driven photodetectors have wide applications in wireless sensor networks and wearable physiological monitoring systems. While 2D materials have different bandgaps for potential novel application fields, the self-driven photodetectors are mainly built on PN junctions or heterostructures, whose fabrication involves doping or reliable multiple transfer steps. In this study, a novel metal–semiconductor–metal (MSM) WSe₂ photodetector with asymmetric contact geometries is proposed. A high responsivity of 2.31 A W⁻¹ is obtained under zero bias, and a large open-circuit voltage of 0.42 V is achieved for an MSM photodetector with a large contact length difference. The MSM photodetector can overcome the disadvantage of high dark current in traditional MSM photodetectors. A small dark current of ≈1 fA along with a high detectivity of 9.16 × 10¹¹ Jones is achieved. The working principles and finite element analysis are presented to explain the origin of the self-driven property and its dependence on the degree of asymmetry.