Optical properties of amorphous and crystalline FeSi2, TaSi2, MoSi2 and CrSi2 films

The optical properties and the peculiarities of the electron energy spectra of polycrystalline and amorphous TaSi/sub 2/ FeSi/sub 2/, MoSi/sub 2/ and CrSi/sub 2/ films were investigated by means of ellipsometric technique. Polycrystalline state in these disilicides was produced by the annealing of as deposited amorphous films at different temperatures and various gas media. The peculiarities of the experimental optical conductivity and imaginary part of the dielectric function spectra were explained on the basis of comparison with the results of the theoretical first-principle calculations of the corresponding functions using LMTO method. It was shown that optical properties of the investigated disilicides in amorphous state differ drastically from the crystalline ones: absorption bands of crystalline phases are smeared, decreased in intensity; the appearance or vanishing of the absorption bands is possible. The analyses of the changes of the interband absorption caused by polycrystalline-amorphous phase transition allows study of the evolution of the corresponding electronic states, It was determined that the series of amorphous states of the investigated silicides, which are indistinguishable using the traditional X-ray methods, possess significantly different optical properties. The reason for such a phenomenon we connect with differences in the short range order of these amorphous states. This fact opens new perspectives of using the optical spectroscopy as a sensitive indirect tool for registration of slight changes in atomic structure of silicides during heat treatments.