Refractive index of porous silicon

Abstract

The optical properties of porous silicon layer described as a mixture of air, silicon, and silicon dioxide are determined by the thickness, porosity, refractive index, and the shape and size of pores. Refractive index of porous silicon is reviewed in this chapter. Full theoretical solutions can be provided by different effective medium approximation methods such as Maxwell-Garnett's, Looyenga's, or Bruggeman's. In the case of semiempirical approaches, the refractive indices are measured using spectroscopic ellipsometry, and then, the model parameters, such as the layer thickness and calculated effective dielectric function, are adjusted to fit the spectra. Various methods based on optical transmission and reflection measurements are used to calculate the refractive index data for both fresh and oxidized porous silicon using the envelope, Maxwell-Garnett, and Goodman method. The coherent transfer matrix technique and Heavens theory were used to determine the complex refractive index of porous silicon for the reflectance of an absorbing layer on an absorbing substrate. An ab initio quantum mechanical study of the effects of oxidation process in porous silicon using an interconnected supercell structure and its complex refractive index was compared with experimental data obtained from spectroscopic ellipsometry. The spectroscopic ellipsometry evaluation of a porous silicon multilayer was reported for the preparation of porous silicon multilayer stacks. The effects of oxidation on the Bragg reflector parameters and the variations in the refractive index and thickness after oxidation were reported.