  We find extraordinary behavior of the local two-terminal spin accumulation
signals in ferromagnet (FM)/semiconductor (SC) lateral spin-valve devices. With
respect to the bias voltage applied between two FM/SC Schottky tunnel contacts,
the local spin-accumulation signal can show nonmonotonic variations, including
a sign inversion. A part of the nonmonotonic features can be understood
qualitatively by considering the rapid reduction in the spin polarization of
the FM/SC interfaces with increasing bias voltage. In addition to the sign
inversion of the FM/SC interface spin polarization, the influence of the
spin-drift effect in the SC layer and the nonlinear electrical spin conversion
at a biased FM/SC contact are discussed.
