SPIN LIFETIMES IN DILUTED MAGNETIC SEMICONDUCTOR SPIN SUPERLATTICES

The growth of spin superlattice structures in which spin-up and spin-d own carriers occupy alternating layers in the structure has recently b een reported. We report here measurements of electron and hole spin li fetimes and spin relaxation processes. In dc photoluminescence spectra , both the higher-energy (+1/2,+3/2) and lower-energy (-1/2,-3/2) heav y-hole exciton interband transitions are observed, even though it woul d be energetically favorable for the spin-up carriers to first relax t o the spin-down state before radiative recombination. From the field d ependence of the intensity ratios of these components and a rate equat ion model, we determine the heavy hole tau(hs) and electron tau(es) sp in lifetimes relative to the radiative lifetime tau(r), with tau(hs)/t au(r) almost-equal-to 4.5 and tau(es)/tau(r) almost-equal-to 0.08, so that the heavy-hole spin lifetime is almost-equal-to 50 times longer t han that of the electron. This is attributed to the strain-induced spl itting of the heavy- and light-hole bands, which prevents fast spin re laxation of the holes.