We present ab initio calculations of the spin-dependent electronic transport in Fe/GaAs/Fe and Fe/ZnSe/Fe (001) junctions simulating the situation of a spin-injection experiment. We follow a ballistic Landauer-Buttiker approach for the calculation of the spin-dependent dc conductance in the linear-response regime, in the limit of zero temperature. We show that the bulk band structure of the leads and of the semiconductor, and even more the electronic structure of a clean and abrupt interface, are responsible for a current polarization and a magnetoresistance ratio of almost the ideal 100%, if the transport is ballistic. In particular, we study the significance of the transmission resonances caused by the presence of two interfaces.
Department of Physics National and Kapodistrian University of Athens University Campus GR-157 84 Zografou, Athens