Variation of the parameters and composition of thin films of porous silicon as a result of oxidation: ellipsometric studies

The variation of the optical characteristics of thin films of oxidized porous silicon as a function of the preparation regime and subsequent heat treatment is investigated by ellipsometry. It is shown that the refractive index, optical thickness, and extinction coefficient of porous silicon films decrease monotonically, but the film thickness increases as the degree of oxidation of the silicon base layer increases. An analysis of the film thickness as a function of the degree of oxidation shows that it differs very little from the same dependence for the nonporous film. The composition of the films is determined from the measured refractive index at a wavelength lambda=632.8 nm by means of curves calculated on the basis of the three-component Bruggeman model of the effective medium for layers with different initial porosities. (C) 1999 American Institute of Physics. [S1063- 7826(99)02410-2].