Synergistic Light Localization Enhanced CMOS‐Compatible Detectors With Infrared Detection Wavelength up to 20 µm

Sub‐bandgap photoresponse in silicon (Si) has attracted considerable attention for applications in communication, spectroscopy, and imaging, owing to the on‐chip complementary metal–oxide–semiconductor (CMOS) compatibility and scalability of Si. Introducing impurity states into crystalline Si provides an effective route to enable such sub‐bandgap absorption. However, conventional Si detectors based on impurity‐state transitions suffer from intrinsically weak optical absorption and substantial photon loss at material interfaces in the very long wavelength infrared (VLWIR) regime, severely limiting their detection sensitivity. Here, we propose a synergistic light localization‐enhanced Si‐based infrared detector with a response extending up to 20 µm, in which a resonant cavity and an interface sub‐wavelength structure are employed to enhance light confinement in the active region. The fabricated device exhibits a peak responsivity of ∼296.9 mA W −1 at λ = 18 µm, a low dark current of ∼3.1 nA, and a peak detectivity of ∼1.9×10 11 cm Hz 1/2 W −1 at 10 K. Furthermore, we demonstrate the potential of the detector for deep‐space applications through neural network‐based recognition and grayscale image reconstruction. The proposed investigation establishes a viable strategy for high‐performance and CMOS‐compatible VLWIR detectors, accelerating the deployment of Si optoelectronics in observational astronomy.