Infrared (IR) absorption and polarized Raman spectra were measured in BaSi2 epitaxial films to investigate the vibrational modes and the symmetry of Si4 cluster in BaSi2. By an analysis based on Raman and/or IR activity in the spectra, the symmetry of Si4 cluster was determined as Th-symmetry and the observed Raman lines and IR peaks were assigned to Ag, Eg, Fg, and Fu, respectively. In the three Raman lines of Fg-mode, one LO phonon line and two TO phonon lines were classified by the depolarization ratio of polarized Raman intensities.

The determination of Raman modes in the range between 280 and 500 cm−1 for a BaSi2(100) epitaxial film on a Si(001) substrate has been accomplished by polarized Raman measurements using a crystal rotation method. The six Raman lines from Si clusters in BaSi2 were observed in the range. In the analysis of their intensity changes as a function of crystal rotation angle based on the Raman tensors of the Si cluster, the six Raman internal modes of A1 (1), E (2), and F2 (3) were completely assigned to the observed Raman lines.

Polarized Raman spectra of a β-FeSi2(100)//Si(001) epitaxial film grown by molecular beam epitaxy were measured to identify the Raman mode of the observed Raman active lines. Twelve of the observed 18 Raman lines showed a clear dependence of the Raman intensity on the crystal rotation angle. By factor group analysis using the orthorhombic symmetry D2h18 of β-FeSi2, five Raman lines (193, 200, 249, 401, 494 cm-1) and seven lines (175, 277, 284, 298, 327, 410, 442 cm-1) were completely assigned to the Ag and B3g modes, respectively. The depolarization ratio of Raman scattering intensities was obtained from polarized Raman spectra measured in two polarization configurations. The values of the depolarization ratio also support the assignment of the Ag and B3g modes in β-FeSi2.

Direct transition energy (Eg) of β-FeSi2/Si(111) epitaxial films grown at different growth temperatures (Ts) was investigated by photoreflectance (PR) measurements. In Raman spectra, the wavenumber of Ag-mode in Fe-Fe and Si-Si vibrations shifted to higher wavenumber with decrease of Ts. The estimated Si/Fe composition ratio of the epitaxial layer became small (Si-poor) in the films grown at lower Ts. In PR spectra, Eg shifted to higher energy with decrease of Ts. These results show that the modification of electronic structure by a strain induced at β-FeSi2/Si hetero-interface is suppressed by an increase of Si vacancies in β-FeSi2.

Direct transition energy (Eg) of β-FeSi2/Si(111) epitaxial films grown at different growth temperatures (Ts) was investigated by photoreflectance (PR) measurements. In Raman spectra, the wavenumber of Ag-mode in Fe-Fe and Si-Si vibrations shifted to higher wavenumber with decrease of Ts. The estimated Si/Fe composition ratio of the epitaxial layer became small (Si-poor) in the films grown at lower Ts. In PR spectra, Eg shifted to higher energy with decrease of Ts. These results show that the modification of electronic structure by a strain induced at β-FeSi2/Si hetero-interface is suppressed by an increase of Si vacancies in β-FeSi2.