SPIN RELAXATION OF 2-DIMENSIONAL ELECTRONS IN GAAS QUANTUM-WELLS

An extremely fast spin relaxation of two-dimensional electrons has bee n observed in undoped GaAs quantum wells. We present experimental evid ence which shows that the fast intrinsic electron spin relaxation in G aAs quantum wells, at low temperatures and in the limit of weak scatte ring, is dominated by the conduction-band spin splitting in III-V comp ounds. We also show that in the limit of strong scattering, at high ex citation intensity or in quantum wells with considerable imperfections , the electron spin relaxation is dominated by an exchange process. Th e spin exchange energy of the heavy-hole exciton of a 15-nm GaAs quant um well is estimated to be 35 (+/-15) mueV.