  We demonstrate the injection and transport of spin-polarized electrons
through n-type doped silicon with in-plane spin-valve and perpendicular
magnetic field spin precession and dephasing ("Hanle effect") measurements. A
voltage applied across the transport layer is used to vary the confinement
potential caused by conduction band-bending and control the dominant transport
mechanism between drift and diffusion. By modeling transport in this device
with a Monte-Carlo scheme, we simulate the observed spin polarization and Hanle
features, showing that the average transit time across the short Si transport
layer can be controlled over 4 orders of magnitude with applied voltage. As a
result, this modeling allows inference of a long electron spin lifetime,
despite the short transit length.
