Probing the optimal refractive index profile of disordered silicon nanowires for photon management applications

Controlling the light transport using photonic structures is essential for the deterministic control of light trapping and that depends on the nano-scale spatial modulation of refractive index. Here, we study the optimal effective refractive index profile (n_eff) of vertically-aligned disordered silicon nanowires using the measured spatial-and wavelength-dependent micro-reflectivity values across the nanowire length. A multi-layer model for the nanowire sample is employed to calculate the reflectivity values using the different n_eff profiles. The calculated reflectivity values are compared with the measured reflectivity values for different polarization states of light. The results validate that the silicon nanowires with an exponential n_eff profile suppress more than 90% reflectivity over a wide angular range for both polarization states of light. Moreover, the nanowires sample with an exponential n_eff profile shows a significant enhancement in light trapping and Raman scattering.