Growth condition dependence of direct bandgap in β-FeSi2 epitaxial films grown by molecular beam epitaxy

Direct bandgap energy (Eg) and lattice deformations were investigated in β-FeSi2 epitaxial films grown by molecular beam epitaxy (MBE) with different growth condition. As Si/Fe flux ratio during the MBE growth became smaller than Si/Fe = 2.0, the lattice constants deviated from those of β-FeSi2 single crystal, which indicated an enhanced lattice deformation at the lower Si/Fe ratio. In photoreflectance (PR) measurements, the PR spectra shifted to lower photon energy with the enhanced lattice deformation. These results revealed that the Eg of β-FeSi2 epitaxial film was modified by the lattice deformation depending on the growth condition.