  Spin accumulation in a paramagnetic semiconductor due to voltage-biased
current tunneling from a polarized ferromagnet is experimentally manifest as a
small additional spin-dependent resistance. We describe a rigorous model
incorporating the necessary self-consistency between electrochemical potential
splitting, spin-dependent injection current, and applied voltage that can be
used to simulate this so-called "3T" signal as a function of temperature,
doping, ferromagnet bulk spin polarization, tunnel barrier features and
conduction nonlinearity, and junction voltage bias.
