Investigation of optical anisotropy of refractive-index-profiled porous silicon employing generalized ellipsometry

Porosity depth profiles in porous silicon were realized by time modulation of the applied current density during electrochemical etching of crystallin e silicon. The samples were investigated by variable angle spectroscopic el lipsometry. Using a basic optical model based on isotropy assumptions and t he Bruggeman effective medium approximation, deviations from an ideal profi le in terms of an interface roughness between the silicon substrate and the porous silicon layer and a compositional gradient normal to the surface we re revealed. Furthermore, optical anisotropy of the sample was investigated by generalized ellipsometry. The anisotropy was found to be uniaxial with the optic axis tilted from surface normal by about 25 degrees. The material was also found to exhibit positive birefringence.