Perspectives of Silicon for Future Spintronic Applications From the Peculiarities of the Subband Structure in Thin Films

The two-band k·p model for the conduction band is used to analyze the subband structure in (001) thin silicon films. In contrast to the usually assumed parabolic energy dispersion, the two-band k·p model is able to describe the conduction band structure in the presence of shear strain. It is demonstrated that the unprimed subbands are degenerate only in relatively thick relaxed films. In thin films, the subbands develop different in-plane effective masses. In orthogonal magnetic fields, this leads to a subband splitting linear in the field strength. It also results in a large subband splitting that is observed in [110]-oriented point contacts. With shear strain, the degeneracy between the unprimed subbands in (001) films is lifted. This splitting depends strongly on the film thickness and becomes large in ultrathin films. Strain-induced valley splitting results in reduced scattering and increased spin coherent time, which makes silicon attractive for future spintronic applications.