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

Abstract

LO-phonon Ramsn scattering has been observed with GaAs quantum wells where the incident and scattered photon energies are both resonant with an exciton transition. This very strong single phonon intrinsic effect, called “doubly resonant Raman scattering” (DRRS), does not exist in intrinsic bulk GaAs. The largest DRRS was observed with the scattered photon at the n=1 heavy hole free exciton E 1h and incident photon at the nominally forbidden transition involving the n=1 electron and n=3 heavy hole E 13h when E 1h + h ̵ ;ω LO = E 13h where h ̵ ω LO = 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 Fröhlich interaction can account for the observed strength and that as expected the deformation potential contribution is negligible. Also, relaxation effects are identified in these Raman spectra.