Resonance Raman Scattering by Confined LO and TO Phonons in GaAs-AlAs Superlattices

It is shown that in GaAs-AlAs superlattices the confined longitudinal-optic Raman phonons created via either deformation-potential or Fröhlich electron-phonon interaction are different. This effect is demonstrated by comparison of resonance and off-resonance Raman spectra. Phonons of $A_1$ symmetry (point group $D_{2d}$) dominate in resonance, while $B_2$ phonons are stronger in the off-resonance case. The resonance profile of the $A_1$ modes is discussed. We also report the observation of confined transverse-optic phonons under extremely resonant conditions.