Enhancement and suppression of spin density polarization due to inhomogeneous electric fields*

We report on a theoretical and computational study of the spin polarization propagation in charge and spin inhomogeneous semiconductor structures. We use a self-consistent, semiclassical approach based on the Boltzmann transport equation to calculate the spin density imbalance, $\delta n_{s}$, defined as $\delta n_{s}=n_{\uparrow}-n_{\downarrow}$, and the spin density polarization, $P_{s}$, defined as the ratio $P_{s}=\delta n_{s}/n$, where $n$ is the total charge density, in the presence of inhomogeneous electric fields. We find that the spin-polarized transport can be drastically enhanced or suppressed by inhomogeneous electric fields, such as those arising at semiconductor interfaces. Furthermore, we find that the spin density imbalance, $\delta n_{s}$, and spin density polarization, $P_{s}$, have diametrally opposite dependence on doping concentrations and charge inhomogeneous distributions. This is in contrast to the common assumption in the literature that these two quantities essentially have the same spin relaxation lengths.