Spin lifetimes in diluted magnetic semiconductor spin superlattices

Abstract

The growth of spin superlattice structures in which spin-up and spin-down carriers occupy alternating layers in the structure has recently been reported. We report here measurements of electron and hole spin lifetimes and spin relaxation processes. In dc photoluminescence spectra, both the higher-energy (+1/2,+3/2) and lower-energy (-1/2,-3/2) heavy-hole exciton interband transitions are observed, even though it would be energetically favorable for the spin-up carriers to first relax to the spin-down state before radiative recombination. From the field dependence of the intensity ratios of these components and a rate equation model, we determine the heavy hole τhs and electron τes spin lifetimes relative to the radiative lifetime τr, with τhs/τ r≊4.5 and τes/τr≊0.08, so that the heavy-hole spin lifetime is ≊50 times longer than that of the electron. This is attributed to the strain-induced splitting of the heavy- and light-hole bands, which prevents fast spin relaxation of the holes.