A self-driven photodetector based on a SnS ₂/WS ₂ van der Waals heterojunction with an Al ₂O ₃ capping layer

Photodetectors based on two-dimensional (2D) materials have attracted considerable attention because of their unique properties. To further improve the performance of self-driven photodetectors based on van der Waals heterojunctions, a conductive band minimum (CBM) matched self-driven SnS ₂/WS ₂ van der Waals heterojunction photodetector based on a SiO ₂/Si substrate has been designed. The device exhibits a positive current at zero voltage under 365 nm laser illumination. This is attributed to the built-in electric field at the interface of the SnS ₂ and WS ₂ layer, which will separate and transport the photogenerated carriers, even at zero bias voltage. In addition, the Al ₂O ₃ layer is covered by the surface of the SnS ₂/WS ₂ photodetector to further improve the performance, because the Al ₂O ₃ layer will introduce tensile stress on the surface of the 2D materials leading to a higher electron concentration and smaller effective mass of electrons in the films. This work provides an idea for the research of self-driven photodetectors based on a van der Waals heterogeneous junction.