RESONANT RAMAN LINE-SHAPE OF OPTIC PHONONS IN GAAS ALAS MULTIPLE-QUANTUM WELLS/

We study the dependence of the optic phonon Raman line shape of GaAs/A lAs multiple quantum wells on photon energy and AlAs layer thickness. Broad features due to the forbidden interface modes, observed more str ongly for outgoing than for incoming resonance, are induced by elastic scattering of the photoexcited exciton. The interface feature in the GaAs-like phonon region has several minima due to anticrossings of its dispersion with the odd-order confined modes. This corrects previous interpretations of these structures as due to higher even-order confin ed modes.