Ballistic spin injection from Fe into ZnSe(001), (111), and (110), and into GaAs(001)

We present first-principles calculations of ballistic spin injection in Fe/GaAs and Fe/ZnSe junctions with orientations (00 1), (111), and (I 10). We find that the symmetry mismatch of the Fe minority spin states with the semiconductor conduction states can lead to extremely high spin polarization of the current through the (001) interface for hot and thermal injection processes. Such a symmetry mismatch does not exist for the (I 11) and (I 10) interfaces, where smaller spin injection efficiencies are found. The presence of interface states at the Fermi energy is found to lower the current spin polarization.