  We study the evolution and distribution of non-equilibrium 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. The electric
field distribution and spin polarization distribution are calculated
numerically. 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.
