FEMTOSECOND SPECTROSCOPY OF CARRIER-SPIN RELAXATION IN GAAS-ALXGA1-XAS QUANTUM-WELLS

We investigate the spin relaxation of optically excited charge carriers in a variety of GaAs-Al(x)Ga(1-x)As quantum wells and superlattices at low temperatures by ultrafast time-resolved photoluminescence spectroscopy. Structures with uniform static optical properties show a markedly varied spin scattering in the time domain, thereby requiring a series of studies with systematically modified epitaxial growth conditions. A multiexponential spin relaxation is seen in quantum wells with a fast initial component of less than 1 ps and a subsequent relaxation within approximately 150 ps. For the same growth conditions, the polarization decay time in superlattices approaches bulk values, indicating a dimensionality dependence of the spin scattering.