Si nanowires versus Si bulk systems: a comparative study of their optical properties

We theoretically investigate the effects of the embedding media and the geometrical sizes on the optical properties of a periodic square array of Si nanowires (NWs). We compare the above properties with those of Si bulk film. This simulated system is made of four stacked layers along a semi-infinite air space. The stacked layer system is defined by a transparent layer of ITO, the active layer of Si NWs embedded into the filling medium, the polymer layer PMMA and the substrate of SiO2. The Si bulk film system is also characterized by the same layers, but the active layer is constituted by the Si bulk instead of Si NWs. The multilayer absorbance is simulated by the Transfer Matrix Method, while the Si NW system is treated as an homogeneous layer whose effective dielectric function is described by the Bruggeman model. For both s- and p-polarizations at normal and oblique incidences, we report a typical oscillating behavior in the absorbance/reflectance spectra, regardless of the type of system (Si film or Si NWs), the type of embedding medium and sizes in Si NWs. Greater diameter-to-periodicity ratio (D/P) for longer Si NWs benefit the light absorption up to 80 per cent in the VIS range. Indeed, the absorbance values of the Si NW system are higher than those of the Si bulk film when the amount of silicon material is identical in both systems.

Si nanowires versus Si bulk systems: a comparative study of their optical properties Articles