Optical modeling of black silicon using an effective medium/multi-layer approach

In this work, black silicon (BSi) structures including nanocones and nanowires are modeled using effective medium theory (EMT), where each structure is assumed to be a multilayer structure of varying effective index, and its optical scattering in the infrared range is studied in terms of its total reflectance, transmittance and absorptance using the transfer matrix method (TMM). The different mechanisms of the intrinsic absorption of silicon are taken into account, which translates into proper modeling of its complex refraction index, depending on several parameters including the doping level. The model validity is studied by comparing the results with the rigorous coupled wave analysis and is found to be in good agreement. The effect of the aspect ratio, the spacing between the structure features and the structure disordered nature are all considered. Moreover, the results of the proposed model are compared with reflectance measurements of a fabricated BSi sample, in addition to other measurements reported in the literature for Silicon Nanowires (SiNWs). The TMM along with EMT proves to be a convenient method for modeling BSi due to its simple implementation and computational speed. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.