  An investigation was carried out into the effect of spin drift on spin
accumulation signals in highly-doped Si using non-local 4-terminal (NL-4T) and
3-terminal (NL-3T) methods. The spin signals in the NL-4T scheme were not
affected by spin drift, and the bias dependence was governed by whether spins
were injected into or extracted from the Si channel. In contrast, the spin
signal was strongly modulated by the bias electric field in the NL-3T scheme.
The bias electric field dependence of the spin signals in the NL-3T method was
quantitatively clarified using the spin drift-diffusion equation, and the
results can be reasonably explained.
