We directly imaged electrical spin injection and accumulation in the gallium arsenide channel of lateral spin-transport devices, which have ferromagnetic source and drain tunnel-barrier contacts. The emission of spins from the source was observed, and a region of spin accumulation was imaged near the ferromagnetic drain contact. Both injected and accumulated spins have the same orientation (antiparallel to the contact magnetization), and we show that the accumulated spin polarization flows away from the drain (against the net electron current), indicating that electron spins are polarized by reflection from the ferromagnetic drain contact. The electrical conductance can be modulated by controlling the spin orientation of optically injected electrons flowing through the drain.

We show that the accumulation of spin-polarized electrons at a forward-biased Schottky tunnel barrier between Fe and n-GaAs can be detected electrically. The spin accumulation leads to an additional voltage drop across the barrier that is suppressed by a small transverse magnetic field, which depolarizes the spins in the semiconductor. The dependence of the electrical accumulation signal on magnetic field, bias current, and temperature is in good agreement with the predictions of a drift-diffusion model for spin-polarized transport.