Optical functions and their empirical modeling for beta-FeSi2 thin epitaxial films on Si(111)

The real and imaginary parts of the dielectric function epsilon (E) = epsil on (1) (E) + i . epsilon (2)(E) were calculated from reflection spectra of iron disilicide (beta -FeSi2) epitaxial film's with use of the Kramers-Kron ig integral relations in the 0.1-6.2 eV energy range at room temperature. A semiempirical model of the dielectric function for the beta -FeSi2 epitaxi al films was derived on the basis of the known theoretical calculations of the energy band structure of beta -FeSi2 single crystals and the data of th e optical transmittance and reflectance spectroscopy. The integrated spectr a of the dielectric function were decomposed into the contributions from si x noninteracting harmonic oscillators and the parameters of these oscillato rs were evaluated. A satisfactory agreement was obtained between the experi mental spectra and the spectra of complex refraction index and reflectance coefficient as calculated on the basis of the model suggested.