Resonant first- and second-order raman scattering in GaP

The dependence on laser frequency of the scattering cross section for allowed and forbidden first-order Raman scattering and for second-order scattering is presented. The measurements were performed in the vicinity of the E0 and E0+Δ0 gaps. It is shown that the Γ15 components of the Raman tensor exhibit a sharp resonance at E0 while Γ1 components resonate both at E0 and E0+Δ0. The results are interpreted in terms of a theory which assumes parabolic bands extending to infinity. The second-order scattering is produced mainly by electron-two-phonon interaction vertices, except for the strongly resonant sharp peaks which correspond to the creation of two LO phonons with k→0 (Γ1) and one LO plus one TO phonon with k→0 (Γ15). From these measurements, values for the electron-two-phonon deformation potentials are obtained.