Identification of Vibrational Modes in BaSi₂ Epitaxial Films by Infrared and Raman Spectroscopy

Abstract

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.

Influence of Ba-to-Si deposition rate ratios on the electrical and optical properties of B-doped BaSi2 epitaxial films

“…We observed five peaks which originate from the internal vibrations of Si tetrahedra in the BaSi2 lattice. 28) For samples grown under Si-rich conditions, RBa/RSi = 1.0 and 1.4, the transverse optical phonon line of Si (SiTO) was observed. The absorption coefficient of BaSi2 at a wavelength of the excited laser light (532nm) is α = 3×10 5 cm −1 .…”

Simple way of finding Ba to Si deposition rate ratios for high photoresponsivity in BaSi2 films by Raman spectroscopy

“…In all of the samples, we observed five distinct peaks assigned to the internal vibrations of Si tetrahedra [28][29][30][31] with Th symmetry in the lattice of BaSi2. 32 Here, focusing on the Si-rich side, the transverse optical phonon line of Si (SiTO) was observed at RBa/RSi ≤ 1.5 for the 580 °C samples, wherein the photoresponsivity reached a maximum at RBa/RSi = 2.2, i.e., slightly higher than 1.5. The absorption coefficient of BaSi2 at a wavelength of the excited laser light (532 nm) is α = 3 × 10 5 cm −1 , 2 hence, the penetration depth of the laser light was limited to approximately 1/α × 3 ≈ 0.1 μm.…”

Effect of post-annealing on the significant photoresponsivity enhancement of BaSi2 epitaxial films on Si(111)

“…We observed five peaks assigned to Ag, Eg, and Fg (dotted lines) in all the samples which originate from the internal vibrations of Si tetrahedral in the BaSi 2 lattice. 41) It is noted that the TO phonon line of Si (Si TO ) was observed for samples at T a = 600 °C and 800 °C and the photoresponsivities of these samples were quite low in Fig. 1, whereas the Si TO peak was not detected in the other samples.…”