  The temperature evolution of spin relaxation time, {\tau}sf, in degenerate
silicon (Si)-based lateral spin valves is investigated by means of the Hanle
effect measurements. {\tau}sf at 300 K is estimated to be 1.68+-0.03 ns and
monotonically increased with decreasing temperature down to 100 K. Below 100 K,
in contrast, it shows almost a constant value of ca. 5 ns. The temperature
dependence of the conductivity of the Si channel shows a similar behavior to
that of the {\tau}sf, i.e., monotonically increasing with decreasing
temperature down to 100 K and a weak temperature dependence below 100 K. The
temperature evolution of conductivity reveals that electron scattering due to
magnetic impurities is negligible. A comparison between {\tau}sf and momentum
scattering time reveals that the dominant spin scattering mechanism in the Si
is the Elliott-Yafet mechanism, and the ratio of the momentum scattering time
to the {\tau}sf attributed to nonmagnetic impurities is approximately
3.77*10^-6, which is more than two orders of magnitude smaller than that of
copper.
