Interference effects: A key to understanding forbidden Raman scattering by LO phonons in GaAs

We show that the contributions of intrinsic and impurity-induced forbidden LO-phonon Raman scattering in GaAs can be quantitatively separated by investigating interference effects between allowed and forbidden LO-phonon scattering. We perform a new calculation of impurity-induced scattering and determine the resonance profile for GaAs near the $E_0$+${\Delta }_0$ gap. Comparison with experiment shows that impurity-induced scattering plays a dominant role. Absolute values of the Raman efficiencies are estimated and compared with experiment.