The temperature and doping dependence of inverse spin Hall effect in n-GaAs*

We have carried out measurements of the inverse spin Hall effect (ISHE) in a series of n-GaAs epilayers doped near the metal-insulator transition. Spin currents are generated using epitaxial Fe/GaAs (001) Schottky tunnel barriers. The ISHE is detected in a simple Hall cross geometry, and precession in a static magnetic field (the Hanle effect) is used to separate the effect from background contributions. We find that the ISHE voltage at low temperatures is much larger than expected based on previous measurements of the direct spin Hall effect. The enhancement is accompanied by significant distortion of the Hanle curves, suggesting that hyperfine interactions play a significant role. Comparison with non-local spin valve measurements over the entire doping range (3 x 10^16 cm^-3 to 7 x 10^16 cm^-3) and at temperatures up to 110 K indicates that local inhomogeneities in the hyperfine field, which disappear as the temperature increases, may be responsible for the enhancement.