Resonance-Enhanced Black Phosphorus Mid-Infrared Photodiode with Nanosecond Response and High Responsivity at Room Temperature

Room-temperature mid-infrared (MIR) photodetectors are crucial for a wide range of applications, including free-space communication, infrared countermeasures, and gas sensing. Recently, two-dimensional (2D) materials have emerged as promising candidates for next-generation MIR detection. However, simultaneously achieving high responsivity and fast response speed in 2D material-based MIR detectors remains challenging. Here, we demonstrate a high-performance vertical black phosphorus (BP) photodiode that integrates Schottky-contacted, plasmonic-resonated bottom electrodes with an ultrashort vertical channel. This design synergistically enhances the MIR light absorption area and carrier transport by spatially aligning the plasmonic hot spots with the Schottky junction, enabling efficient carrier generation and rapid extraction. Our proposed photodetector achieves a responsivity of 5 A/W, representing a two-order enhancement compared with the devices without plasmonic integration and corresponding to a specific detectivity of 5.0 × 10⁹ cm Hz¹/² W^-1. More importantly, it also achieves an ultrafast rise/decay time of 22/26 ns at 3.7 μm, setting a benchmark for room-temperature MIR photodetection in 2D material systems. This vertical device architecture, leveraging a high Schottky barrier height and strong localized electric fields induced by the plasmonic resonance, offers a scalable and promising strategy for high-performance room-temperature MIR photodetectors that simultaneously achieve a high photoresponse and ultrafast speed.