Zone-center Phonon Frequencies Research Articles

PHONON SOFTENING IN ULTRA HEAVILY DOPED Si AND Ge

Multiple pulse annealing with a XeCl laser (308 nm, 10nsec, ~0.8J/cm2) has been used to produce flat concentration profiles following heavy implantations of Ga, B, P, and As at energies up to 350 keV. The influence of the free carrier concentration on the zone center phonon frequency has been studied by Raman scattering with violet and ultra-violet cw laser lines to ensure that only the implanted region was sampled. We find a softening of the zone center optic mode in Si : As (Ne ≈ 3 x 1021 cm-3) of ~10 cm-1 and for Si : B (Np ≈ 1 x 1021 cm-3) a softening of ~20 cm-1.

Zone-Centre Lattice Vibrations in α-Sulphur Including Effects of Hydrostatic Pressure

The zone-centre phonon frequencies in orthorhombic sulphur have been calculated at hydrostatic pressures of 0 kbar, 5 kbar and 10 kbar by applying a dynamical model which includes both external and internal vibrational degrees of freedom of the molecular motion. The calculations are carried out within the harmonic approximation with the intermolecular force constants calculated using a 6-exp atom-atom potential function and with the intramolecular force constants found from spectroscopic studies. Results are compared with those from a rigid molecule model calculation and from experiment. An analysis of the calculated eigenvectors predicts that not all the modes can be classified in the conventional way, as either internal or external, but for some modes both types of motion contribute substantially. Some suggestions are made for improving the dynamical model in order to remove the discrepancies between theory and experiment found in the frequency splittings of the high-frequency intramolecular modes.

Tetragonal SrTiO3 revisited: The effect of impurities on the Raman spectrum

Abstract We report an exhaustive study of the tetragonal phase of SrTiO 3 by Raman scattering. This work is compared with the results of neutron inelastic scattering, infrared, and electric field induced Raman scattering experiments to give a coherent picture of the zone centre phonon frequencies. The results of Raman scattering from isomorphous compounds confirm this picture.

Dielectric screening and zone-center phonons in Si

We present a microscopic calculation of the zone-center phonon frequencies of silicon. The electronic contributions to the phonons are fully incorporated into the dynamical matrix via the dielectric matrix ${\ensuremath{\epsilon}}_{\stackrel{\ensuremath{\rightarrow}}{\mathrm{G}},\stackrel{\ensuremath{\rightarrow}}{\mathrm{G}}}$. The acoustic sum rule is shown to be satisfied.

Raman scattering and infrared reflectivity in GeSe

Raman and infrared-active zone-center optical phonon frequencies and dielectric constants of single-crystal, orthorhombic, germanium selenide (GeSe) are reported. The number of phonons observed for given polarization configurations is consistent with group-theoretical predictions. The near-degeneracy of some Raman and infrared modes suggests a dominance of intra-layer, compared to inter-layer, forces characteristic of “layer-type” compounds.