  A large spin-accumulation voltage of more than 1.5 mV at 1 mA, i.e., a
magnetoresistance of 1.5 {\Omega}, was measured by means of the local
three-terminal magnetoresistance in nondegenerate Si-based lateral spin valves
(LSVs) at room temperature. This is the largest spin-accumulation voltage
measured in semiconductor-based LSVs. The modified spin drift-diffusion model,
which successfully accounts for the spin drift effect, explains the large
spin-accumulation voltage and significant bias-current-polarity dependence. The
model also shows that the spin drift effect enhances the spin-dependent
magnetoresistance in the electric two terminal scheme. This finding provides a
useful guiding principle for spin metal-oxide semiconductor field-effect
transistor (MOSFET) operations.
