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

We propose a gold - based nanostructured design for achieving enhanced absorption in ultrathin black phosphorus (BP) layers in the 3 - 5 μm 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 μm. We test the efficiency of these absorbers by computing their absorption enhancement factor and comparing it against the conventional 4n
²
limit. For a BP layer thickness of 5 nm, we are able to achieve an enhancement of 561 at a wavelength of 4 μm, which is significantly greater than the conventional value of 4 n
²
equal to 34 for an isolated textured BP layer.