We investigate the spin-resolved dynamics of spin-polarized carriers injected via a ferromagnetic scanning-tunnelling-microscope tip (STM tip) into uniformly and non-uniformly n-doped bulk semiconductor - externally driven by a current source. We propagate the injected spin packets (assumed gaussian in space at t = 0) by considering a spin hydrodynamic approach based on balance equations directly derived from a spin-dependent Boltzmann equation. We determine the spin-polarization landscapes (time and position) of the carrier population $(n_(\uparrow}-n_{\downarrow})/(n_{\uparrow}+n_{\downarrow}$ and the current density $(j_{\uparrow}-j_{\downarrow})/(j_{\uparrow}+j_{\downarrow})$. While in the uniformly-doped system the carrier spin-polarization has a slow decay, in the non-uniformly doped system it shows a drastic fall down in the interface. In contrast the current spin-polarization exhibits an enhancement for both of the systems particularly in the interface.
Spin polarized transport; Semiconductors; Interfaces; Electrical injection
