Three essential elements of a functional semiconductor spin transport device are i) an efficient mechanism for electrically injecting spin-polarized electrons into a semiconductor, ii) a practical means for spin manipulation and transport, and iii) a simple electronic scheme for detecting the resulting spin polarization. This talk will address each of these three elements in turn using data from low-temperature scanning magneto-optical Kerr microscopy studies. In these experiments, we directly image the spin polarization resulting from electrical injection and subsequent transport of spin-polarized electrons in lateral devices having iron (Fe) Schottky tunnel-barrier contacts on a lightly-doped n-type GaAs channel [1]. At a source contact, the 2-D images reveal efficient electrical spin injection extending out to 120 microns in the n:GaAs channel, as well as an accumulation of spin-polarized electrons within a spin diffusion length of a drain contact. Finally, we use both optical and all-electrical studies to show that these Fe/GaAs Schottky tunnel barrier contacts can also be used as electrical spin detectors in addition to their role as spin injectors. By tuning the voltage bias across the tunnel barrier, it is possible to tune both the magnitude as well as the sign of the spin-detection sensitivity. All these experiments are conducted in a geometry that is sensitive only to electron spin precession, allowing for detailed modeling of spin transport in the channel based on spin drift-diffusion equations.
[1] X. Lou et al, Nature Physics v3, p197 (2007); S.A. Crooker, M. Furis, X. Lou, C. Adelmann, D.L. Smith, C.J. Palmstrom & P.A. Crowell, Science v309, p2191 (2005).