Gate-Tunable van der Waals Photodiodes with an Ultrahigh Peak-to-Valley Current Ratio.

Photodetectors and imagers based on 2D layered materials are currently subject to a rapidly expanding application space, with an increasing demand for cost-effective and lightweight devices. However, the underlying carrier transport across the 2D homo- or heterojunction channel driven by the external electric field, like a gate or drain bias, is still unclear. Here, a visible-near infrared photodetector based on van der Waals stacked molybdenum telluride (MoTe 2 ) and black phosphorus (BP) is reported. The type-I and type-II band alignment can be tuned by the gate and drain voltage combined showing a dynamic modulation of the conduction polarity and negative differential transconductance. The heterojunction devices show a good photoresponse to light illumination ranging from 520-2000 nm. The built-in potential at the MoTe 2 /BP interface can efficiently separate photoexcited electron-hole pairs with a high responsivity of 290 mA W -1 , an external quantum efficiency of 70%, and a fast photoresponse of 78 µs under zero bias.