Effect of free charge carriers on birefringence and dichroism in anisotropic porous silicon layers

The infrared optical properties of anisotropic mesoporous silicon films containing free charge carriers (holes) are studied experimentally and theoretically. The results of simulation of the optical properties of the produced samples in the effective-medium approximation show a heavy dependence of the birefringence, reflection anisotropy, and dichroism on the concentration of free charge carriers. The unsteady behavior of the differential transmittance recorded for the samples at mutually perpendicular polarization directions of light are attributed to the effect of charge carriers with a concentration on the order of 10$^{19}$ cm$^{-3}$. The results of the study suggest that anisotropic silicon nanostructures are promising materials for infrared photonics and terahertz engineering.