Effective light polarization insensitive and omnidirectional properties of Si nanowire arrays developed on different crystallographic planes

摘要： In this paper, fabrication of vertical Si nanowire arrays (SiNWAs) by a facile metal assisted electroless etching approach on different crystallographic planes of Si has been reported. A very low specular reflectance (Rspec) of 0.04% and 0.03% has been achieved in the whole visible range for SiNWAs grown on Si(100) and Si(111) oriented substrates, respectively. High broadband enhancement has been detected for vertical SiNWAs due to multiple scattering paths inside the nanowire arrays. On the other hand, inclined nanowires showed a fascinating behavior at the longer wavelength regime, where light gets the longer path to reflect back-forth and ease to reflect back outward at normal incidence. Moreover, for [100] SiNWAs, transverse electric (TE) field component demonstrates the strong polarization insensitive properties at the expense of transverse magnetic (TM) field component with a minimum reflectance of < 2% up to 1200 nm. The [100] SiNWAs demonstrates extra-ordinary omnidirectional properties at θB ≥ 58o. Theoretical validation of COMSOL with an effective medium approach reveal the effective dipole coupling and the presence of strong absorption modes for vertical SiNWs at a typical wavelength regime. The highly bound states of the particle tunneling through classical forbidden region shows a strong enhancement in light absorption effect.