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We study the possibility of spin injection from Fe into Si(001), using theSchottky barrier at the Fe/Si contact as tunneling barrier. Our calculationsare based on density-functional theory for the description of the electronicstructure and on a Landauer-Buttiker approach for the current. Thecurrent-carrying states correspond to the six conduction band minima of Si,which, when projected on the (001) surface Brillouin zone (SBZ), form fiveconductance hot spots: one at the SBZ center and four symmetric satellites. Thesatellites yield a current polarization of about 50%, while the SBZ center can,under very low gate voltage, yield up to almost 100%, showing a zero-gateanomaly. This extremely high polarization is traced back to the symmetrymismatch of the minority-spin Fe wavefunctions to the conduction bandwavefunctions of Si at the SBZ center. The tunneling current is determined bythe complex band structure of Si in the [001] direction, which showsqualitative differences compared to that of direct-gap semiconductors.Depending on the Fermi level position and Schottky barrier thickness, thecomplex band structure can cause the contribution of the satellites to beorders of magnitude higher or lower than the central contribution. Thus, byappropriate tuning of the interface properties, there is a possibility to cutoff the satellite contribution and to reach high injection efficiency. Also, wefind that a moderate strain of 0.5% along the [001] direction is sufficient tolift the degeneracy of the pockets so that only states at the zone center cancarry current.

Spin injection from Fe into Si(001): ab initio calculations and role of the Si complex band structure