Ellipsometry and ab initio approaches to the refractive index of porous silicon

Abstract

Spectroscopic ellipsometry is used to determine the complex refractive index(n−ik), porosity, and thickness of porous silicon (PSi) films. These films are obtained by anodizingp-type crystalline silicon in a hydrofluoric acid bath. After etching, PSi samples are heated to750 °C in a controlled oxygen environment. A detailed analysis of the ellipsometry data is performed inorder to determine the complex refractive index of PSi thin film. This frequency dependence ofn and k is compared with the results of ab initio quantum mechanical calculations carried out bymeans of CASTEP codes within the density functional theory. The theoretical results showa diminution of the lattice constant as the oxygen content grows, in contrast to thehydrogen-saturated surface case.