Spin-dependent scattering in the presence of polarized nuclei in n-GaAs

We report on all-electrical measurements of the inverse spin Hall effect (ISHE) in epitaxial (100) Fe/GaAs heterostructures with a channel doping (Si) of $n =5\times 10^{16}$~cm$^{-3}$ and highly doped Schottky tunnel barriers. Under measurement conditions of large (10-20\%) spin accumulation at the injection electrode, a significant dynamic nuclear polarization (DNP) enhances the size of the ISHE. The electron spin dynamics are shown to match the predictions of the usual drift-diffusion model, including the applied, hyperfine, and Knight fields. The DNP, however, also enhances the scattering of spin-polarized carriers, which is not understood. To separate the roles of the electronic and nuclear spin systems, we have employed a pump-probe method to vary the nuclear spin polarization $\langle I \rangle$ and electron spin polarization $S$ independently. The size of the ISHE is proportional to $\langle I \rangle$ when the DNP is small, but it eventually saturates. When the nuclear polarization is fixed, the ISHE is linear in $S,$ as expected. We conclude therefore that the measured signal scales linearly with the spin current multiplied by a transport skewness parameter that depends strongly on $\langle I \rangle$.