Spin injection from Fe into Si(001):Ab initiocalculations and role of the Si complex band structure

Abstract

We study the possibility of spin injection from Fe into Si͑001͒, using the Schottky barrier at the Fe/Si contact as tunneling barrier. Our calculations are based on density-functional theory for the description of the electronic structure and on a Landauer-Büttiker approach for the current. The current-carrying states correspond to the six conduction-band minima ͑pockets͒ of Si, which, when projected on the ͑001͒ surface Brillouin zone ͑SBZ͒, form five conductance hot spots: one at the SBZ center and four symmetric satellites. The satellites 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-gate anomaly. This extremely high polarization is traced back to the symmetry mismatch of the minority-spin Fe wave functions to the conduction-band wave functions of Si at the SBZ center. The tunneling current is determined by the complex band structure of Si in the ͓001͔ direction, which shows qualitative differences compared to that of direct-gap semiconductors. Depending on the Fermi level position and Schottky barrier thickness, the complex band structure can cause the contribution of the satellites to be orders of magnitude higher or lower than the central contribution. Thus, by appropriate tuning of the interface properties, there is a possibility to cut off the satellite contribution and to reach high injection efficiency. Also, we find that a moderate strain of 0.5% along the ͓001͔ direction is sufficient to lift the degeneracy of the pockets so that only states at the zone center can carry current.

Interplay of growth mode and thermally induced spin accumulation in epitaxialAl/Co2TiSi/AlandAl/Co2TiGe/Alcontacts

“…The resulting heterostructure, Al/Heusler/Al/Si, would certainly require a careful choice of the thickness of the second Al layer, which acts as buffer between the Heusler alloy and the semiconductor. For a thin Al layer, the situation corresponds to a ballistic spin injection similar to that investigated theoretically by Mavropoulos for the Fe/Si system, 48 and could be treated by a similar method as employed here. Alternatively, the thickness of the Al can be even larger, though not exceeding the spin relaxation length.…”

Information Processing With Pure Spin Currents in Silicon: Spin Injection, Extraction, Manipulation, and Detection

“…This was accomplished in a lateral transport geometry using lithographic techniques compatible with existing device geometries and fabrication methods. Although the measurements reported here were performed at low temperature to reduce the noise arising from the relatively high Fe/Al 2 O 3 contact resistance, techniques to reduce the interface resistance [34] or take advantage of fundamental band structure symmetries between Fe and Si [35] offer promising avenues to significantly improve the signal to noise for room temperature operation.…”

Electrical spin injection in p-type Si using Fe/MgO contacts

“…This is consistent with a recent report showing that the crystalline quality of AlO x tunnel barrier can have an important effect on the efficiency of creating the spin accumulation 32 . Just as in a MgO-based MTJ [8][9][10] , the spin filtering effect in tunnel contacts on Si is guaranteed by the 4-fold in-plane crystalline symmetry of the epitaxial MgO(001) barrier and its relationship with the bcc Fe electrode 33 . This leads to the conservation of the symmetry of the Bloch states at the Fermi level in the MgO layer, and as a consequence a higher tunnel spin polarization is observed.…”