A simple 230 MHz photodetector based on exfoliated WSe 2 multilayers.

We demonstrate 230 MHz photodetection and a switching energy of merely 27 fJ using WSe 2 multilayers and a very simple device architecture. This improvement over previous, slower WSe 2 devices is enabled by systematically reducing the RC constant of devices through decreasing the photoresistance and capacitance. In contrast to MoS 2 , reducing the WSe 2 thickness toward a monolayer only weakly decreases the response time, highlighting that ultrafast photodetection is also possible with atomically thin WSe 2 . Our work provides new insights into the temporal limits of pure transition metal dichalcogenide photodetectors and suggests that gigahertz photodetection with these materials should be feasible.