  The spin-orbit interaction in a solid couples the spin of an electron to its
momentum. This coupling gives rise to mutual conversion between spin and charge
currents: the direct and inverse spin Hall effects. The spin Hall effects have
been observed in metals and semiconductors. However, the spin/charge conversion
has not been realized in one of the most fundamental semiconductors, silicon,
where accessing the spin Hall effects has been believed to be difficult because
of its very weak spin-orbit interaction. Here we report observation of the
inverse spin Hall effect in silicon at room temperature. The spin/charge
current conversion efficiency, the spin Hall angle, is obtained as 0.0001 for a
p-type silicon film. In spite of the small spin Hall angle, we found a clear
electric voltage due to the inverse spin Hall effect in the p-Si film,
demonstrating that silicon can be used as a spin-current detector.
