HgCdTe mid-Infrared photo response enhanced by monolithically integrated meta-lenses

Area of Science:

• Optoelectronics
• Nanotechnology
• Infrared detection

Background:

• Reducing photodetector photosensitive area suppresses dark current but lowers light absorptance, degrading specific detectivity (D*).
• Monolithic integration of meta-lenses with photodetectors offers a potential solution to enhance performance.

Purpose of the Study:

• To propose and demonstrate a polarization-independent dielectric meta-lens monolithically integrated with a HgCdTe infrared photodetector.
• To enhance the photodetector's performance by concentrating light onto a reduced photosensitive area.

Main Methods:

• A meta-lens composed of nano-pillars with varying diameters was fabricated by carving the CdZnTe substrate of the HgCdTe detector in situ.
• The meta-lens focuses incident light through the CdZnTe medium onto the HgCdTe photosensitive region.

Main Results:

• The integrated meta-lens achieved a wavelength-sized focal spot with over 63% focusing efficiency.
• For a reduced photosensitive area of 5 μm × 5 μm, light absorptance was maintained above 50% (49x higher than without meta-lens).
• Dark current was reduced by 16-64 times, and specific detectivity (D*) was enhanced by 5.5 times.
• The meta-lens showed good dispersion tolerance from 3.3 μm to 5 μm, with an average D* enhancement of 3 times.
• The angle of view was 4.0° or 7.7° for a 5 μm × 5 μm photosensitive area, depending on focal length.

Conclusions:

• The monolithic integration of a dielectric meta-lens with a HgCdTe photodetector effectively enhances performance.
• This approach overcomes the trade-off between reduced dark current and light absorptance in smaller photosensitive areas.
• The meta-lens integrated detector demonstrates significant improvements in specific detectivity and maintains good optical performance over a broad wavelength range.