Valley splitting in Si quantum dots embedded in SiGe

TL;DR

This study uses atomistic calculations to analyze valley splitting in silicon quantum dots within SiGe buffers, revealing how dot thickness and buffer disorder influence valley degeneracy lifting, crucial for quantum computing applications.

Contribution

It provides detailed atomistic insights into how quantum dot thickness and buffer disorder affect valley splitting, guiding experimental design for qubit stability.

Findings

Valley splitting exceeds 150 ueV for dots thinner than 6 nm.

Buffer disorder reduces valley splitting by a factor of 2.5.

Splitting fluctuates by about 20 ueV across disorder realizations.

Abstract

We examine energy spectra of Si quantum dots embedded into Si_{0.75}Ge_{0.25} 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 ueV. 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 ~20 ueV for different disorder realizations. Through these simulations we can guide future experiments into regions of low device-to-device fluctuations.