Resonant Raman scattering by plasmons and LO phonons near theE1andE1+

Wolfgang Kauschke

¹

,

N. Mestres

²

,

M. Cardona

³

Abstract

We report on the resonance of Raman scattering by plasmons near the E& and E& +A~gaps of heavily doped n-type GaSb. The dipole-allowed Raman scattering by plasmons due to the electro-optic (Frohlich interband) coupling of bands interferes with the dipole-forbidden qdependent Frohlich intraband scattering.Absolute values of Raman polarizabilities and efficiencies are displayed. The interference is compared with that of the LO phonons seen from the surface depletion layer. Theoretical expression for the resonance of the di6'erent scattering mechanisms (electro-optic, Frohlich intraband, electric field induced, deformation potential, impurity induced, 2LO) near the E& and E&+6& gaps are derived and compared with the experiment. The dispersion of the second-order susceptibility 7'&23(coL, -Qp, Q)g) is displayed and the Faust-Henry coe%cient of CiaSb determined.

Allowed and forbidden Raman scattering mechanisms for detection of coherent LO phonon and plasmon-coupled modes in GaAs

“…Raman scattering by the LO phonon and LOPC modes of III-V compound semiconductors can have contributions from a variety of dipole-allowed and dipole-forbidden Raman scattering processes 22,23,[27][28][29][30][31][32][33][34] , which are summarized in Table I. For the (001) surface of a zinc blende or diamond structure crystal, the dipole-allowed first-order Raman tensor for LO phonon scattering is the off-diagonal tensor of eq.…”

“…By contrast, the L+ branch can be considered as purely plasmonic. Since no ionic deformation is present for plasmons, only the EO mechanism, which is associated with their electric field, is operative in the dipole-allowed Raman scattering 22,23 .…”

“…Since the EO effect contributes only to the LO and not to the TO phonons, the ratio of a DP and a EO can be experimentally obtained from the ratio of the LO and TO Raman intensities 22,23,28,29,32,33 . The EO contribution to the allowed scattering by the LO phonon is usually small compared with the DP contribution 23,29 .…”

“…Because of the formation of the depletion or accumulation layer at the surface, the LOPC mode properties can be strongly depth-dependent in the surface region through the free carrier concentration. For example, LO phonons couple with doped electron plasma in the bulk of n-doped III-V semiconductors, but remain uncoupled (unscreened) in the depletion region where the carrier concentration is low 22,23 .…”

“…When optical excitation occurs near a critical point in the joint density of initial and final states, q-dependent Raman scattering by LO phonons can occur in dipole-forbidden geometries via the intraband Fröhlich (F) and FranzKeldysh (FK) mechanisms 23 . Near the E 0 and E 1 critical points of a zinc blende crystal, the forbidden scattering is described by a diagonal tensor of eq.…”