We present a detailed study of the anisotropic optical properties of mesoporous silicon layers prepared from substrates having different doping levels under various preparation conditions. We demonstrate that the morphology of the layers strongly depends on the preparation conditions. It correlates with measured optical anisotropy values and defines the directions of the optical axes. The experimental data are explained in the framework of an effective medium model which takes into account the different morphologies of the layers, Modifications of the optical anisotropy of the layers in a controlled manner by filling the pores with dielectric substances and by oxidation of the structure confirm that form birefringence is the origin of the optical anisotropy.
Kunzner, N., Diener, J., Gross, E., Kovalev, D., Timoshenko, V. Y., & Fujii, M. (2005). Form birefringence of anisotropically nanostructured silicon. Physical Review B, 71(19). https://doi.org/10.1103/PhysRevB.71.195304