Effects of photon enhanced lifetime and form anisotropy in silicon nanowire arrays on efficiency of nonlinear-optical processes

Abstract

Arrays of silicon nanowires (SiNWs) of about 100 nm in diameter formed by metal-assisted chemical etching of crystalline silicon (c-Si) substrates were studied regarding efficiency of optical interactions in them. Strong scattering in the SiNW arrays results in enhanced photon lifetime in them, which was evidenced by measurement of the cross-correlation function for femtosecond pulses scattered by the SiNW arrays. This effect results in an order of magnitude growth of efficiency such processes as spontaneous Raman scattering and third-harmonic (TH) generation compared to the signals for c-Si. Using (110) oriented c-Si substrate we managed to make well-oriented tilted SiNWs demonstrating strongly anisotropy of the TH and coherent anti-Stokes Raman scattering signals. In particular, efficiencies of these processes differ significantly when incident radiation propagates along or perpendicular to the SINWs. The obtained results could be explained by variations of the local fields in SiNWs and scattering cross-section.