Spin-injection through an Fe/InAs Interfaces 

             �c���DMaciej Zwierzycki



  Faculty of Applied Physics and MESA+, 

   University of Twente, The Netherlands



  Institute of Molecular Physics, P.A.S., Smoluchowskiego 17,

  60-179 Poznan, Poland 

 

  Current interest in spin-injection into semiconductors is motivated

  both by the fundamental aspects of the phenomenon and by potential

  applications. The basic obstacle to spin-injection from a metallic

  ferromagnet into a semiconductor is the large difference in their

  conductivities; the resistivity of a semiconductor such as InAs is

  much larger than either the majority- or minority-spin resistivity

  of Fe. However, the spin-dependent interface resistance if

  sufficiently large could generate a spin-dependent potential drop at

  the interface. Here, we evaluate this term for an Fe/InAs interface

  from first principles. The formalism based on the tight-binding

  linear-muffin-tin orbital surface Green's function method allows us

  to treat large lateral superlattices so that we can study the

  influence of disorder on the conductance. We find that due to the

  symmetry mismatch in the minority-spin channel the specular

  interface acts as an efficient spin filter with the polarisation of

  transmitted current close to 100%.  The resistance of a diffusive

  interface is comparable to the resistance of an InAs slab several

  hundreds nanometers thick but the symmetry breaking due to the

  disorder can substantially reduce the spin-asymmetry. We conclude

  that the spin injection for this system is possible only if the

  interface disorder is not too large.