Ultrafast Hot Carrier Cooling Enabled van der Waals Photodetectors at Telecom Wavelengths

Two-dimensional (2D) materials with high carrier mobility and picosecond intrinsic response times exhibit large potential for fast optoelectronics operating at telecom wavelengths. However, due to the inefficient utilization of hot carriers, 2D photodetectors for the telecom C-band have rarely been realized. Here, we report a high-performance and waveguide-free WS₂/graphene photodetector operating at 1560 nm enabled by hot carrier injection and long-lived charge separation. The efficiently injected hot electrons from graphene to WS₂ exhibit ultrafast cooling dynamics with a 3 ps intrinsic response time. Simultaneous hole trapping in WS₂ ensures a long circulation of injected electrons, enabling a high responsivity of 0.26 A/W. In continuation, we present a vertical WS₂/graphene/WSe₂ device with a built-in electric field and the same detection mechanism, for which a photocurrent on-off ratio of 3500 and an extrinsic response time of 1.71 ns are obtained. Our study highlights the benefit of combining 2D semiconductors and semimetals for high-speed photodetection.