Optical reflectivity from highly disordered Si nanowire films

In this work we present a study of the reflectivity from highly disordered silicon nanowire films as a function of the wire size. Arrays of Au-catalyzed Si wires with length and diameter ranging from 0.15-0.2 microns and 30-50 nm up to 20-25 microns and 200-250 nm, respectively, were grown on top of either SiO2(1 microns)/Si(100) or Si(100) substrates. The integrated total reflection was measured in the 190-2500 nm spectral range. The results show that, increasing the wire size, the optical behavior of the Si wire film can be gradually tuned from that of an optical coating characterized by a graded effective refractive index to that of an ensemble of diffuse optical reflectors. In addition, we show how the optical analysis provides some important indications concerning the structural properties of the nanowires.