Optical properties of β-FeSi2 films grown on Si substrates with different degree of structural perfection

β-FeSi2 films, distinguished in their crystalline perfection, have been grown under different conditions of Fe and Si deposition on Si substrates. Optical transmittance, reflection, and ellipsometric investigations were carried out from the NIR to UV. Phonon spectra were studied by FTIR transmittance measurements. The spectral distribution of optical constants shows strongest differences at photon energies <3 eV for films of different structural quality. For MBE films there is considerable fine structure in the optical constants above the gap with pronounced features in between 1 and 2 eV. With higher degree of crystallinity the phonon spectrum becomes increasingly structured.