Mirror‐Integrated Vertical Van der Waals Photodiode for High‐Efficiency, High‐Speed, and Broadband Photodetection

The development of self‐powered photodetectors that simultaneously achieve high quantum efficiency and fast response remains a fundamental challenge in optoelectronics, primarily due to the intrinsic trade‐off between photon absorption depth and carrier transit distance. Here, we present a vertical van der Waals photodiode architecture that overcomes this limitation through a synergistic photon recycling and vertical extraction mechanism. By integrating a WSe 2 /MoS 2 heterojunction directly on a metal‐mirror electrode, we concurrently enhance optical absorption while establishing a nanoscale vertical transport channel that minimizes carrier transit time. This dual‐function design enables a record external quantum efficiency of 84% at zero bias, a fast response time of ∼200 ns, a specific detectivity of 1.6 × 10 11 cm Hz 1/2 W −1 , and a power conversion efficiency of 11.2%. Benefitting from the type‐II band alignment heterostructure, the vertical vdW photodiode achieves broadband detection from visible (633 nm) to the near‐infrared region (1550 nm). This work provides a generalizable device strategy for developing next‐generation, high‐performance, and low‐power optoelectronic systems.