Band-gap modifications of beta-FeSi2 with lattice distortions corresponding to the epitaxial relationships on Si(111)

Electronic bands nearby the gap for several strained structures corresponding to the epitaxial relationships of β-FeSi2 on Si(111) have been calculated by first-principles density-functional method. We have also estimated the related elastic energies, where optimization in the strained structures has been allowed for lattice parameters and for atomic positions. Only one of the heavily strained structures corresponding to β-FeSi2(101) and (110)//Si(111), still the most frequently occurring structures in both epitaxial layers and precipitates, displays a sizable change in gap nature. We show that this issue can be interpreted by the unexpected anisotropic behavior of the band gap for uniaxial lattice distortions along the b and c sides, which are actually very close in size.