Microstructure based optical modeling of ZnO- porous silicon permeated nanocomposites

ZnO composites with porous silicon (PSi) are increasingly used in advanced optical and electronic structures. ZnO/PSi nanocomposites have been prepared by permeating anodized PSi with ZnO sols based on zinc acetate. Upon thermal annealing the ZnO sols form surface wurzite nanocrystals, as indicated by XRD from annealing temperatures of 400 °C. By increasing the annealing up to 800 °C, electron microscopies evidence that ZnO diffuses through the columnar PSi, while void ZnO crystallites decorate the surface. Angular dependent x-ray photoelectron spectra agree with the partial coverage of the PSi surface by disperse ZnO nanocrystals. In depth composition, analyzed using C-resonant backscattering spectroscopy confirms an activation of ZnO diffusion and PSi oxidation at high temperatures. This microstructural information was used to analyse the optical properties through models adapted to critical processing temperatures. A uniaxial anisotropic layer, included to consider columnar PSi, and an evolution of optical coefficients in agreement with thermally induced effects (namely PSi oxidation and ZnO diffusion-transformation) allows to satisfactorily simulate ellipsometric spectra. The results are relevant for the optimization of bifunctional electronic-antireflective ZnO/PSi structures.