Observation of doubly resonant LO-phonon Raman scattering with GaAs-Al(x)Ga(1-x)As quantum wells.

It is shown that LO-phonon Raman scattering when the incident and scattered photon energies are both resonant with an exciton transition can be very intense. This effect, called "Doubly Resonant Raman Scattering" (DRRS), has been observed with GaAs quantum wells and does not exist in 3D-systems. The largest DRRS was observed with the scattered photon at the n=1 heavy hole free exciton epsilon(1b) and incident photon at the nominally forbidden transition involving the n=1 electron and n=3 heavy hole epsilon(13h) when epsilon(1h) + hbaromega(LO = epsilon (13(h) where hbaromegaLO =36.7 meV is the LO-phonon frequency of GaAs. The sharp DRRS line for the principal sample studied has nearly three times the circular polarization of the broad ordinary luminescence and a large linear polarization (optical alignment) not usually seen in the luminescence of quantum wells. From a theoretical treatment for the first order DRRS, it is concluded that the Frohlich interaction can account for the observed strength and that the deformation potential contribution is negligible. However, the polarization relaxation data suggest that as much as 55% impurity-assisted Frohlich scattering may be present.