An All‐Silicon Metalens Integrated with a Mid‐Wave Infrared Black Phosphorus Photodiode

Abstract Black phosphorus (BP) is a promising material for mid‐wave infrared (MWIR) photodetection because of its direct tunable bandgap and compatibility with a wide range of substrates, particularly silicon. However, optical signal collection in BP devices can be limited by its absorber thickness or active area. Dielectric metasurface lenses, which can be directly integrated into a device's substrate, are a scalable approach to increase the signal collected by BP photodetectors. This work presents the design, fabrication, and characterization of an all‐silicon metasurface lens for focusing MWIR light through its substrate. Then, a BP‐MoS₂ heterojunction photodetector is integrated with the metalens, and MWIR photodetection increases at room temperature. These results demonstrate that integrated metasurface lenses are an excellent approach for boosting the performance of MWIR BP photodetectors.