SPIN DYNAMICS IN DOPED AND INTRINSIC GAAS QUANTUM-WELLS

We have determined the spin relaxation dynamics of electrons, holes an d excitons in GaAs quantum wells by means of subpicosecond studies of the photoluminescence polarization. Our measurements demonstrate that the usual image of instantaneous hole-spin relaxation is not valid in 2D systems. For electrons, the spin relaxation rate is considerably la rger than the corresponding value in p-doped bulk GaAs. The processes of spin relaxation of free excitons are far more complicated than thos e of free carriers: we find that many-body effects play an important r ole in the spin relaxation of excitons.