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

• The metalens is integrated into Ge-based BIB photosensitive elements firstly. • The focused spot is near the diffraction limit , with a focusing efficiency of 42.22%. • For a 3 × 3 array, the average optical crosstalk is remarkably low at only 1.2 %. • The metalens focuses 120 μm THz light, achieving a maximum absorptance of 10.12 %. • Absorptance with the metalens is 30.35 times higher than that without the metalens. 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.