Mid-infrared transmission enhancement through sub-wavelength metal hole array using impedance-matching dielectric layer

The mid-infrared transmission through a 3.7 mum period, two-dimensional sub-wavelength Au metallic hole array integrated on a GaSb/InAs strained layer superlattice nBn photodetector is measured. The surface plasmon-polariton excitation on the Au film induces a peak transmission in the 200 K detector response at 4.2 mum. This transmission is enhanced threefold by the insertion of a SiN_x layer between the Au film and the substrate for impedance matching analogous to antireflection coating.