Efficient light trapping in the infrared using gold – black phosphorus nanostructured absorbers

Abstract

We propose a gold – based nanostructured design for achieving enhanced absorption in ultrathin black phosphorus (BP) layers in the 3 – 5 $\mu$ m wavelength range. By suitably tuning the design parameters, we are able to excite strongly localized modes in BP layers of thicknesses ranging from 5 to 50 nm at a wavelength of 4 $\mu$ m. We test the efficiency of these absorbers by computing their absorption enhancement factor and comparing it against the conventional 4n2 limit. For a BP layer thickness of 5 nm, we are able to achieve an enhancement of 561 at a wavelength of 4 $\mu$ m, which is significantly greater than the conventional value of 4 n2 equal to 34 for an isolated textured BP layer.