ABSTRACT
In combination with ordinary di¥usive transport theory, knowledge of the relevant spin lifetimes allows us to identify the critical length scales for a spin transport device. že relevant spin relaxation mechanisms are reviewed by Fabian in this volume. In the doping range of interest for us, the dominant channel of spin relaxation is the D’yakonov-Perel’ (DP) mechanism [7], which corresponds to the randomization of spin during di¥usive transport by precession around the instantaneous spin-orbit ¢eld. že bulk Dresselhaus spin-orbit coupling (due to the absence of inversion symmetry in GaAs) leads to a rapid decrease, proportional to ne−2 , in the spin lifetime with increasing electron concentration ne [2,4,7]. že strong dependence on carrier density re¦ects the k3 dependence in the spin-orbit Hamiltonian. A maximum in the spin lifetime τs ∼ 100 ns occurs at the MIT (2 × 1016 cm−3) at low temperatures, with a di¥erent set of mechanisms limiting the lifetime at lower dopings [4]. že characteristic length scales for spin transport in the semiconductor are the spin di¥usion length λ τs sD= and driª length ld = μEτs. že characteristic mobility of n-GaAs at the MIT is of order 5000 cm2/V s. Assuming a barely degenerate electron gas one ¢nds that λs is on the order of several microns.
