  Direct visualizations of spin accumulation due to the enhanced spin Hall
effect (SHE) in bismuth (Bi) - doped silicon (Si) at room temperature are
realized by using helicity-dependent photovoltage (HDP) measurements. Under
application of a dc current to the Bi-doped Si, clear helicity-dependent
photovoltages are detected at the edges of the Si channel, indicating a
perpendicular spin accumulation due to the SHE. In contrast, the HDP signals
are negligibly small for phosphorus-doped Si. Compared to a platinum channel,
which has a large spin Hall angle, more than two-orders of magnitude larger HDP
signals are obtained in the Bi-doped Si.
