Ellipsometric studies of porous silicon

Multiple-angle-of-incidence (MAI) ellipsometry at 632.8 nm is used to characterize P and P⁺ porous silicon of high porosity. Complex dielectric constants are obtained, from which the porosity can be estimated qualitatively. The properties of the imaginary part of the dielectric constants are studied and the possible causes are discussed. Two dielectric constants, perpendicular and parallel to the interface, respectively, are measured based on a semi-infinite anisotropic model. Ellipsometric studies demonstrate a larger difference between the two dielectric constants in P⁺ porous silicon, but both P and P⁺ samples only show weak anisotropy, i.e., a network-like structure, which tends towards isotropy, is more suitable for porous silicon than a column-like one, which shows strong anisotropy.