Splitting Valleys in Si/SiO$_2$: Identification and Control of Interface States

Interface states in a silicon/barrier junction break the silicon valley degeneracy near the interface, a desirable feature for some Si quantum electronics applications. Within a minimal multivalley tight-binding model in one dimension, we inspect here the spatial extent of these states into the Si and the barrier materials, as well as favorable conditions for its spontaneous formation. Our approach---based on Green's-function renormalization-decimation techniques---is asymptotically exact for the infinite chain and shows the formation of these states regardless of whether or not a confining electric field is applied. The renormalization language naturally leads to the central role played by the chemical bond of the atoms immediately across the interface. In the adopted decimation procedure, the convergence rate to a fixed point directly relates the valley splitting and the spread of the wave function, consequently connecting the splitting to geometrical experimental parameters such as the capacitance of a two-dimensional electron gas---explicitly calculated here. This should serve as a probe to identify such states as a mechanism for enhanced valley splitting.