RESONANT INTERFERENCE EFFECTS IN THE PHONON RAMAN-SPECTRA OF (311) GAAS ALAS SUPERLATTICES/

We study the dependence on laser frequency (omega(L)) of the Raman spe ctra of GaAs/AlAs superlattices (SL's) grown along the [311] direction . The observed phonon modes follow the polarization selection rules pr edicted by the SL crystal symmetry and, at the highest omega(L), the i ntensities predicted by the bulk Raman tensor. For lower omega(L) we o bserve a complex variation in the intensities of the confined LO and T O modes which deviates sharply from these predictions. We interpret th ese deviations as due to interference between a background associated with the E1 and E1 + DELTA1 gaps and a resonant contribution arising f rom the hh2 --> e2 transition of the SL, both induced by the deformati on potential interaction. For the latter, the electron-phonon coupling with the hole bands is diagonal, in contrast to the off-diagonal (hh --> lh) coupling of conventional (100) SL's. Evidence for a Frohlich i nduced resonance at the E0 + DELTA0 gap of the SL's is also obtained.