Optical functions of epitaxial β-FeSi2 on Si(001) and Si(111)

We accurately measured the complex refractive index and dielectric functions from 0.2 to 5 eV of high-quality β-FeSi2 epitaxial films, with thicknesses ranging from 100 Å to 8000 Å, grown on Si(001) and Si(111) using two different techniques. Reflectance, transmittance and spectroscopic ellipsometry were used and the spectra were analyzed within a multilayer model, by checking the Kramers-Kronig consistency of the derived optical functions. These functions, compared with previous results for polycrystalline samples, showed a very good agreement with those obtained for bulk samples and a significant difference to films. The nature (direct or indirect) of the lowest optical gap and the effects of the film thickness and the substrate orientation on the optical response were also investigated.