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 $E_0$ and $E_0+{\Delta }_0$ gaps. It is shown that the ${\Gamma }_{15}$ components of the Raman tensor exhibit a sharp resonance at $E_0$ while ${\Gamma }_1$ components resonate both at $E_0$ and $E_0+{\Delta }_0$. 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 $\overrightarrow{\mathrm{k}}\simeq 0\left({\Gamma }_1\right)$ and one LO plus one TO phonon with $\overrightarrow{\mathrm{k}}\simeq 0\left({\Gamma }_{15}\right)$. From these measurements, values for the electron-two-phonon deformation potentials are obtained.