The linear and circular polarizations of exciton luminescence in GaAs/AlGaAs quantum wells

We report on the low temperature linearly and circularly polarized photoluminescence excitation spectra, and on the temporal dependence of the polarized PL in undoped GaAs/A/Gal-,As quantum wells (QW). The polarization excitation spectra &in(Ef) and P&,(Ef), El is the exciting (laser) energy, monitored at the upper energy part of the photoluminescence (PL) band show two bands that are attributed to the (e1:hhl)lS and (el:hhl)2S exciton states. &in(t) and P,+(t) decay much faster than PL(t). These observations are explained by the recombination of delocalized excitons in the high energy side oz the PL band. These excitons can move over large "islands" in the QW plane and have a defined KII. They scatter between the islands and relax by emitting acoustic phonons within the islands where they recombine. The spectral shape of Plin and P&, is thus determine_d by the exciton LA phonon scattering rate and the polarization relaxation time dependences on KII.