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Bias dependence of spin-polarized tunnel current through Fe/GaAs and Fe/GaAs/Fe junctions

Spin polarization of the tunnel current under finite bias voltage is studied theoretically for Fe/GaAs junctions with Schottky barriers and Fe/GaAs/Fe tunnel junctions, using a realistic tight-binding model and linear response theory. Calculating the spin polarization of the tunnel current across the interface as a function of bias voltage, we show that the spin-polarized interface resonant states within the Schottky barrier significantly influence spin-dependent tunnelling. The position of the resonant states depends on the Schottky barrier height, and the spin polarization of the tunnel current can be negative for a rather wide range of bias voltage, depending on the Schottky barrier height. The magnetoresistance of Fe/GaAs/Fe tunnel junctions is also negative under high bias voltage, because of the interfacial resonant states in the GaAs layer. The present results demonstrate the importance of controlling Schottky barrier formation to obtain high spin polarization in Fe/GaAs junctions.