Characterization of the structure and optical properties of micron porous layers on antimony-doped silicon substrates

A real structure and optical properties of micron porous silicon layers on Si(111) (Sb) substrates were studied by the two-crystal X-ray diffractometry and reflectometry, scanning electron microscopy, and infrared spectroscopy methods in a 4000- to 12000-cm-1 frequency range. The porous silicon layers were formed by the electrochemical etching method at a 50-mA/cm2 current in a hydrofluoric acid/ethanol mixture in a ratio of 1 : 1. The structural parameters of the layers are determined, namely, the thickness is 6- 66 μm, the average deformation is ≈4.5 × 10-4, and the density is ≈0.72. It is shown that the studied porous layers can be considered uniform only to some extent. The optical transmission spectra were analyzed within the frameworks of the effective medium model and the refractive index n of the substrate was estimated. It is determined that the Si(111) (Sb) substrates have a pronounced transmission band in the spectral range of 1.05-1.5 μm. To restore the dispersion of optical constants from transmission spectra, the procedure, based on the mathematical treatment with regard to real geometric and physical parameters of several transmission spectra by minimizing functional χ2, was proposed. Possibilities of applying the proposed procedure for determinations of optical characteristics of thin layers and heterostructures are discussed. © Pleiades Publishing, Ltd., 2012.