F. Cerdeira

Interaction between electronic and vibronic Raman scattering in heavily doped silicon

Abstract The asymmetry in the one-phonon Raman lines of heavily doped p-type Si is interpreted as the interference of a continuum of electronic excitations with the phonon line. The dependence of the line shape on the exciting frequency is produced by the different resonant behavior of these two scattering mechanisms.

Resonant Raman scattering in germanium

Abstract We have studied the spectral dependence of the first order Raman scattering cross section of Ge at room and liquid nitrogen temperatures in the energy region containing the E 1 and E 1 + Δ 1 optical gaps. This region was covered by a fine mesh of points obtained from the discrete lines of three gas lasers and a cw continuously tunable dye laser. Only one resonant peak was observed, as opposed to the two peaks that characterise the absorption and reflection spectra in this region. The shape of this resonance peak can be explained as due to the changes in the electronic polarizability produced by phonon-induced wave function mixing of the spin-orbit split Λ valence band doublet. The observed temperature shift in the resonant energy is much smaller than the one predicted from the known shifts of the optical gaps with temperature. Furthermore the resonant peak at room temperature appears shifted to higher energies when compared with the theoretical peak calculated from the room temperature optical constants. The resonant Raman peak appears to shift with increasing temperature by the full thermal expansion effect plus only a fraction of the electron-phonon interaction shift seen in the optical constants.

Elastic constants and Raman frequencies of heavily doped Si under uniaxial stress

It is shown that the effects of doping on the C44 elastic constant and on the Raman frequency of p-type silicon disappear upon application of a stress along [001], with a very similar functional dependence on stress. These experiments prove the intimate relationship between these two phenomena and the degeneracy of the valence bands of silicon.

Pressure dependence of phonon energies at critical points in the Brillouin zone in KTaO3 measured with differential second order raman scattering

Abstract Wavelength modulated Raman scattering was used to study the effects of pressure on the second order spectrum of KTaO 3 . The pressure results lend support to previous identifications of structures in the second order differential Raman spectrum in terms of pairs of phonons from critical points in the Brillouin zone. Using these identification mode Gruneisen parameters are obtained for several vibrational modes. Strong anharmonic behavior of of the TA( X ) mode is observed when we correlate the results from pressure measurements with previous studies of the effects of temperature.

Resonant Raman scattering by plasmons in n-type Ge

Abstract We have measured the Raman efficiency for plasmon scattering in n-type Ge as a function of laser excitation frequency in the range of the E 1 and E 1 +Δ 1 optical gaps (2.1–2.5 eV). Our results can be explained by a mechanism involving the macroscopic electric field that accompanies the plasma oscillation in a manner similar to that responsible for Frohlich-interaction-induced forbidden LO-phonon resonances in polar semiconductors plus some contribution of the standard cdf mechanism for scattering by plasmons.

Light Scattering by Plasmons in Heavily Doped n-Type Ge and Si

We report Raman scattering by plasmons in n-type silicon and its resonant behavior near the E1 gap. The scattering mechanism seems to be similar to the forbidden scattering by LO-phonons in ionic materials.