Electronic structure of epitaxial beta-FeSi2 on Si (111)

We have applied a combination of surface spectroscopy techniques (XPS,Auger,electron energy loss and bresstrahlung isochromat spectroscopy)to investigate the chemical bonding of beta-FeSi_2 thin films epitaxially grown on the Si(111) surface. The local structure of the films has been investigated with the extended BIS fine structure technique. The semiconducting nature of the films is evidenced by a shift of the empty d-band to higher binding energies and by the lowering of the density of states close to E_F as compared to pure Fe films. The dielectric functions extracted from the electron energy loss spectra strongly support this picture. We measured an energy gap of 1.0+-0.2 eV which compares favourably with density of ststes calculations for the beta-FeSi_2 semiconducting phase.