Enhanced valley splitting in Si layers with oscillatory Ge concentration

The valley degeneracy in Si qubit devices presents problems for their use in quantum information processing. It is possible to lift this degeneracy by using the wiggle well architecture, in which an oscillatory Ge concentration couples the valleys. This paper presents the basic theory of this phenomenon together with model calculations using the empirical pseudopotential theory to obtain the overall magnitude of this effect and its dependence on the wavelength of the concentration oscillations. We derive an important selection rule which can limit the effectiveness of the wiggle well in certain circumstances.