Modifications of direct transition energies in β-FeSi₂ epitaxial films grown by molecular beam epitaxy

Modifications of direct transition energies by crystal lattice deformations were confirmed in β-FeSi₂ epitaxial films on Si(111) substrates. With an increasing of annealing temperature (T_a), lattice constants of a-axis expanded, and those of b- and c-axis shrank, resulting in the volume reduction in -0.2%. In photoreflectance measurements, the direct transition energy at Y point in the Brillouin zone of β-FeSi₂ (∼0.92 eV) was shifted to lower photon energy with the increase in T_a. These results revealed that the band-gap energy was modulated systematically by the lattice deformation, which suggests a possibility of band-gap engineering by the lattice deformation in β-FeSi₂ epitaxial films on Si(111) substrates.