Focusing of spin polarization in semiconductors by inhomogeneous doping.

We study the evolution and distribution of nonequilibrium electron spin polarization in n-type semiconductors within the two-component drift-diffusion model in an applied electric field. Propagation of spin-polarized electrons through a boundary between two semiconductor regions with different doping levels is considered. We assume that inhomogeneous spin polarization is created locally and driven through the boundary by the electric field. We show that an initially created narrow region of spin polarization can be further compressed and amplified near the boundary. Since the boundary involves variation of doping but no real interface between two semiconductor materials, no significant spin polarization loss is expected. The proposed mechanism will be therefore useful in designing new spintronic devices.