  Spin transport in non-degenerate semiconductors is expected to pave a way to
the creation of spin transistors, spin logic devices and reconfigurable logic
circuits, because room temperature (RT) spin transport in Si has already been
achieved. However, RT spin transport has been limited to degenerate Si, which
makes it difficult to produce spin-based signals because a gate electric field
cannot be used to manipulate such signals. Here, we report the experimental
demonstration of spin transport in non-degenerate Si with a spin
metal-oxide-semiconductor field-effect transistor (MOSFET) structure. We
successfully observed the modulation of the Hanle-type spin precession signals,
which is a characteristic spin dynamics in non-degenerate semiconductor. We
obtained long spin transport of more than 20 {\mu}m and spin rotation, greater
than 4{\pi} at RT. We also observed gate-induced modulation of spin transport
signals at RT. The modulation of spin diffusion length as a function of a gate
voltage was successfully observed, which we attributed to the Elliott-Yafet
spin relaxation mechanism. These achievements are expected to make avenues to
create of practical Si-based spin MOSFETs.
