Electric-field-induced Raman scattering in GaAs: Franz-Keldysh oscillations

We have studied the influence of strong electric fields on the Raman scattering intensity from LO phonons in GaAs (100) at room temperature using laser excitation energies above the fundamental ${\mathit{E}}_0$ gap. Striking oscillations are found in the scattering intensity for configurations where either the deformation potential or Fröhlich electron-phonon interaction contribute. The oscillations in the deformation-potential-mediated scattering intensity can be related to Franz-Keldysh oscillations derived from the ${\mathit{E}}_0$ gap, whereas a more complicated mechanism has to be invoked for processes where Fröhlich interaction is responsible.