Electric-field dependent spin diffusion and spin injection into semiconductors

We derive a drift-diffusion equation for spin polarization in semiconductors by consistently taking into account electric-field effects and nondegenerate electron statistics. We identify a high-field diffusive regime which has no analogue in metals. In this regime there are two distinct spin diffusion lengths. Furthermore, spin injection from a ferromagnetic metal into a semiconductor is enhanced by several orders of magnitude and spins can be transported over distances much greater than the low-field spin diffusion length.