  We propose a spin-dependent resonant tunneling structure to efficiently
inject spin-polarized current into silicon (Si). By means of a heavily doped
polycrystalline Si (Poly-Si) between the ferromagnetic metal (FM) and Si to
reduce the Schottky barrier resistance, we estimated raising the tunneling
current density up to $10^8$Am$^{-2}$. The small Fermi sea of the charge
carriers in Si focuses the tunneling electrons to the resonant spin states
within a small region of transverse momentum in the ferromagnet which creates
the spin polarization of the current. Because of the large exchange splitting
between the spin up and down bands, the decay of the spin current is explained
in terms of scattering out of the focused beam. The spin polarization in the
current survives only if the thickness of the FM-layer is smaller than the
spin-diffusion length estimated from that cause.
