  Efficient injection of spin-polarized electrons into the conduction band of
silicon is limited by the formation of a silicide at the ferromagnetic metal
(FM)/silicon interface. In the present work, this "magnetically-dead" silicide
(where strong spin-scattering significantly reduces injected spin polarization)
is eliminated by moving the FM in the spin injector from the tunnel junction
base anode to the emitter cathode and away from the silicon surface. This
results in over an order-of-magnitude increase in spin injection efficiency,
from a previously-reported magnetocurrent ratio of ~2% to ~35% and an estimated
spin polarization in Si from ~1% to at least ~15%. The injector tunnel-junction
bias dependence of this spin transport signal is also measured, demonstrating
the importance of low bias voltage to preserve high injected spin polarization.
