Doubling of conductance steps in Si/SiO2 quantum point contact.

We have calculated the effect of the oxidation-induced strain on the ballistic conductance in a Si/SiO2 quantum point contact. The strain-induced deformation potential was calculated semiempirically using a viscoelastic continuum model. The charge carriers are confined to the corners of the waveguide by both the strain-induced deformation potential and the Si/SiO2 band edge discontinuity. As a consequence nearly degenerate symmetric and antisymmetric transverse states are formed for the Si [001] minima. This additional degeneracy within the Landauer-Büttiker formalism leads to doubling of conductance steps for electrons in the [001] minima which govern the conductance near the cutoff energy. Due to the additional strain-induced confinement, the effective channel width of the quantum point contact is smaller and therefore the conductance steps are sharper. [ABSTRACT FROM AUTHOR]