Photon lifetime correlated increase of Raman scattering and third-harmonic generation in silicon nanowire arrays

Light propagation in silicon nanowire layers is studied via Raman scattering, third-harmonic generation and cross-correlation function measurements. The studied silicon nanowire arrays are characterized by a wire diameter of 50–100 nm and a layer thickness ranging from 0.2–16 μm. These structures are mesoscopic for light in the visible and near infrared ranges. The Raman signal increases monotonically with layer thickness increases at a 1.064 μm pump wavelength. The Stokes component for silicon nanowire arrays with a thickness larger than 2 μm exceeds that for crystalline silicon by more than an order. At the mentioned thicknesses, an increase is also registered for the third-harmonic signal, one that is up to fourfold greater than that for crystalline silicon for a 1.25 μm pump wavelength. Measurements of cross-correlation functions for the scattered photons evidence the significant photon lifetime increase in the silicon nanowire layers at their thickness increase. This fact can be connected with multiple scattering inside the studied mesoscopic structures and the increase of the interaction length for the Raman and third-harmonic generation processes.