Anisotropic Raman excitation of the coupled longitudinal-optical-phonon—plasmon modes inn-GaAs near theE0+Δ0energy gap

A strongly anisotropic Raman excitation of the coupled longitudinal-optical-phonon—plasmon modes in $n$-GaAs near the $E_0+{\Delta }_0$ energy gap has been observed. The anisotropy is shown to result from the interference between the deformation potential and electro-optic mechanism and the electron-charge-density fluctuation mechanism.