OPTICAL-PROPERTIES OF BETA-FESI2 FILMS GROWN ON SI SUBSTRATES WITH DIFFERENT DEGREE OF STRUCTURAL PERFECTION

beta-FeSi2 films, distinguished in their crystalline perfection, have been grown under different conditions of Fe and Si deposition on Si su bstrates. Optical transmittance, reflection, and ellipsometric investi gations were carried out from the NIR to UV. Phonon spectra were studi ed by FTIR transmittance measurements. The spectral distribution of op tical constants shows strongest differences at photon energies <3 eV f or films of different structural quality. For MBE films there is consi derable fine structure in the optical constants above the gap with pro nounced features in between 1 and 2 eV. With higher degree of crystall inity the phonon spectrum becomes increasingly structured.