Spin polarization via electron tunneling through an indirect-gap semiconductor barrier

We study the spin dependent tunneling of electrons through a zinc-blende semiconductor with the indirect X (or Delta) minimum serving as the tunneling barrier. The basic difference between tunneling through the Gamma vs the X barrier is the linear-k spin-orbit splitting of the two spin bands at the X point, as opposed to the k(3) Dresselhaus splitting at the Gamma point. The linear coefficient of the spin splitting at the X point is computed for several semiconductors using density-functional theory and the transport characteristics are calculated using the barrier tunneling model. We show that both the transmission coefficient as well as the spin polarization can be large, suggesting the potential application of these materials as spin filters.