Electron subband structure and controlled valley splitting in silicon thin-body SOI FETs: Two-band k · p theory and beyond

We use a two-band k · p Hamiltonian to describe the subband structure in strained silicon thin films. The model describes the dependence of the transversal effective mass on strain and film thickness. However, it is found that the two-band k · p model is unable to describe recently observed large valley splitting. Therefore a generalization of the model is necessary. To go beyond the k · p theory, an auxiliary tight-binding model defined on a lattice of sites containing two localized orbitals is introduced in such a way that it reproduces the bulk dispersion obtained from the two-band k · p model. Corresponding dispersion relations including strain are obtained. We discuss an alternative mechanism to create and control the valley splitting by applying shear strain. The valley splitting increases with increased shear strain and decreasing film thickness and can be larger than the spin splitting. This makes silicon-based quantum devices promising for future applications in quantum computing.