LONG HOLE SPIN RELAXATION-TIMES IN DILUTED MAGNETIC SEMICONDUCTOR HETEROSTRUCTURES

We report the observation of long spin lifetimes for heavy holes in (Z n,Mn)Se and (Zn,Fe)Se based heterostructures. These long spin relaxati on times are observed in both simple strained epilayers, as well as in complex spin superlattice structures in which the spin up and spin do wn carriers occupy alternating layers of the superlattice. In photolum inescence spectra, both the higher energy (+1/2, +3/2) and lower energ y (-1/2, -3/2) heavy hole exciton interband transitions are observed, even though it would be energetically favorable for the spin up carrie rs to first relax to the spin down state before radiative recombinatio n. From the magnetic field dependence of the intensity ratio of these components and a rate equation model, we find that the heavy hole spin lifetime tau(hs) is substantially longer than the electron spin lifet ime tau(es), with tau(ha)/tau(r) almost-equal-to 4 and tau(es)/tau(r) almost-equal-to 0.06, where tau(r) is the radiative recombination time . This is attributed to the strain induced splitting of the heavy and light hole bands, which inhibits mixing of the hole spin states and su bsequent dipole-allowed transitions producing fast spin relaxation.