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

ABSTRACT: Polarization-independent dielectric meta-lens is proposed to monolithically integrate with a HgCdTe infrared photodetector to concentrate power flux into a reduced photosensitive area for performance enhancement. Although a reduction in photosensitive area could suppress the dark current, the more seriously reduced light absorptance would degrade the specific detectivity D*. The integration of the meta-lens could reverse the situation by improving the absorptance of the photosensitive region. The meta-lens composed of an array of nano-pillars with varying diameters is formed by carving the CdZnTe substrate of the HgCdTe detector so that the integration could be accomplished in situ. The meta-lens focuses the incident light through the CdZnTe medium and at the HgCdTe photosensitive region. The focal spot is about the wavelength size and the focusing efficiency is above 63%. Concerning a HgCdTe detector with a pitch size of 40 ?m?×?40 ?m, when the photosensitive area is reduced to 5 ?m?×?5 ?m, the meta-lens could still keep the light absorptance above 50%, which is 49 times higher than that of the device without the meta-lens. The dark current reduces with the decreasing photosensitive area in a linear manner. When the photosensitive area shrinks from 40 ?m?×?40 ?m to 10 ?m?×?10 ?m or 5 ?m?×?5 ?m, the dark current reduces by 16 or even 64 times. Compared to the pristine device, the employment of the meta-lens together with the reduction in photosensitive area could enhance D* by 5.5 times for the photosensitive area as 5 ?m?×?5 ?m. Further, the meta-lens exhibits a good dispersion tolerance over the wavelength range from 3.3 ?m to 5 ?m. The averaged detectivity enhancement over this spectrum range is around 3 times for the photosensitive area as 5 ?m?×?5 ?m. The angular response of the meta-lens integrated detector depends on the focal length. For a focal length of 73 µm or 38 µm, the angle of view for a 5 ?m?×?5 ?m photosensitive area is 4.0° or 7.7°. For the inter-pillar distance to be 2 µm in our design, the influence of the coupling effect between the nano-pillars on the performance of the meta-lens is little.

SUBMITTER: Li F 

PROVIDER: S-EPMC7156491 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature