Proficiency in light reflectance mitigation is the most crucial factor for high photodetector performance. In this respect light trapping mechanism based on nanostructures or microstructures such as nanopillars, nanocones, nanopyramids have emerged as the most promising candidate for reducing overall light reflectance. This could be attributed to its effective large irradiation area, multiple scattering of incident light as well as increased path length of incident rays in these nanostructures. This paper proposes an optical modelling of a GaAs/GaSb material based vertically oriented core-shell cone topped octagonal shaped nanopillar structure with periodical trapezoidal nanotexturization over it to be deployed over a circular planar detector’s surface of radius 50um. The geometrical analytical investigation of the proposed model exhibits a 0.999 overall absorbance and 0.995A/W photoresponsivity along with 87% EQE at 1um operating wavelength.