Spin injection at Heusler/semiconductor interfaces: First-principles determination of potential discontinuity and half-metallicity

Technologically relevant properties, such as potential discontinuity and half-metallic behavior, are determined by means of an accurate first-principles approach for Co2MnGe/GaAs and Co2MnGe/Ge interfaces. Interface states appear in both sides of the junctions, so that half-metallicity, typical of bulk Co2MnGe, is locally lost. As for the potential discontinuity, the character of the contact is dramatically affected by the semiconductor side: In Co2MnGe/GaAs, irrespective of the atomic termination, the Fermi level is pinned within the energy band gap, whereas it lies close to the valence-band maximum in the case of Co2MnGe/Ge. This gives rise to a rectifying contact in the first case and ohmic for holes in the second case, both potentially useful for spin–injection purposes. Finally, we investigate the effects of possible Co–Mn antisites in bulk Co2MnGe and find that half-metallicity is only locally destroyed, since defect-induced gap states are shown to be screened in a couple of nearest-neighbor atomic shells.