Optical properties of porous silicon. Part III: Comparison of experimental and theoretical results

In our previous study, the refractive indices of freestanding porous silicon (PS) layers were derived using the envelope method, where the computation is based on the values of local minima and maxima in the oscillations of transmission spectra. In the present work, an improved procedure for calculating the optical parameters from the measurements data is described. It is verified by reflection measurements on freestanding samples that optical scattering at the air–PS interface is the main reason for the loss of the transmitted light intensity and thus for the inaccurate results we obtained earlier by the envelope method. This however can be avoided by taking into consideration the relationship between the optical path in the plane-parallel film and the position of extrema in the transmission spectra. The as-determined effective refractive indices show very good matching with the theoretical calculations by the Bruggeman’s effective medium approximation.