Optical performance enhancement of a blocked-impurity-band photodetector integrated with terahertz metalenes

The terahertz (THz) band is widely utilized in space exploration. However, the size of traditional THz detectors impedes their integration into focal plane arrays (FPAs). Advances in metasurface technology have enabled the miniaturization and large-scale integration of THz FPAs. This study demonstrates the integration of a high-resistance silicon metalens with a germanium (Ge)-based blocked-impurity-band (BIB) detector. The metalens, featuring high transmittance, focuses THz light onto a compact photosensitive element, significantly enhancing performance. The focused spot size approaches the diffraction limit, with an average focusing efficiency of 42.22 %. A 3 × 3 metalenses array exhibits excellent optical crosstalk, averaging only 1.2 %. Integration with the metalens reduces the size of the Ge-based BIB detector's photosensitive element to 153.85 μm, achieving an absorptance of 10.12 %, which is 30.35 times higher than that without the metalens. The ultra-thin metalens promotes the miniaturization of BIB detectors, facilitating their large-scale integration into FPAs.