  Spontaneous spin polarization of the electrical current flowing through
nonmagnetic semiconductor junctions can be generated by carrier scattering
processes that are independent of the carrier spin. The two required elements
for current-induced spin polarization are (1) the presence of built-in
spatially-varying electric fields in the junction and (2) energy-dependent
carrier scattering processes. Spin-orbit interactions are not required for this
effect, thus it should occur in materials like silicon that lack significant
spin-orbit interactions. Approximate analytic expressions as well as detailed
numerical simulations of the time-dependent nonlinear spin transport in a GaAs
junction strongly suggest that the recent experimental observation of
current-induced spin polarization in this system [Y. Kato, R. C. Myers, A. C.
Gossard, and D. D. Awschalom, Phys. Rev. Lett. 93, 176601 (2004)] may be
explained by this effect.
