We examine energy spectra of Si quantum dots embedded in Si0.75Ge0.25 buffers using atomistic numerical calculations for dimensions relevant to qubit implementations. The valley degeneracy of the lowest orbital state is lifted and valley splitting fluctuates with monolayer frequency as a function of the dot thickness. For dot thicknesses <= 6 nm, valley splitting is found to be > 150 mu eV. Using the unique advantage of atomistic calculations, we analyze the effect of buffer disorder on valley splitting. Disorder in the buffer leads to the suppression of valley splitting by a factor of 2.5; the splitting fluctuates with approximate to 20 mu eV for different disorder realizations. Through these simulations we can guide future experiments into regions of low device-to-device fluctuations. (C) 2008 American Institute of Physics.
Available at: http://works.bepress.com/gerhard_klimeck/26/