Download from http://link.aps.org/doi/10.1103/PhysRevB.80.201309
Spin injection efficiency is shown to strongly depend on the interfacial structure between Fe contacts and AlxGa1−xAs in spin-based light emitting diodes. Both the magnitude and sign of the injected carriers are dependent on the atomic structure of the contacts and can be controlled through changes in temperature both during and following growth. We propose that the observed dependence is due to phase formation resulting from Fe/GaAs interfacial reactions. This proposed mechanism is consistent with electronic structure calculations, which show that thin layers of DO3 Fe3Ga at the Fe/GaAs interface can produce the observed sign reversals in the spin polarization of injected carriers.