SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits

Thomas McJunkin, Benjamin Harpt, Yi Feng, Merritt P. Losert, Rajib Rahman, J. P. Dodson, M. A. Wolfe, D. E. Savage, M. G. Lagally, S. N. Coppersmith, Mark Friesen (), Robert Joynt and M. A. Eriksson ()
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Thomas McJunkin: University of Wisconsin-Madison
Benjamin Harpt: University of Wisconsin-Madison
Yi Feng: University of Wisconsin-Madison
Merritt P. Losert: University of Wisconsin-Madison
Rajib Rahman: University of New South Wales
J. P. Dodson: University of Wisconsin-Madison
M. A. Wolfe: University of Wisconsin-Madison
D. E. Savage: University of Wisconsin-Madison
M. G. Lagally: University of Wisconsin-Madison
S. N. Coppersmith: University of Wisconsin-Madison
Mark Friesen: University of Wisconsin-Madison
Robert Joynt: University of Wisconsin-Madison
M. A. Eriksson: University of Wisconsin-Madison

Nature Communications, 2022, vol. 13, issue 1, 1-7

Abstract: Abstract Large-scale arrays of quantum-dot spin qubits in Si/SiGe quantum wells require large or tunable energy splittings of the valley states associated with degenerate conduction band minima. Existing proposals to deterministically enhance the valley splitting rely on sharp interfaces or modifications in the quantum well barriers that can be difficult to grow. Here, we propose and demonstrate a new heterostructure, the “Wiggle Well”, whose key feature is Ge concentration oscillations inside the quantum well. Experimentally, we show that placing Ge in the quantum well does not significantly impact our ability to form and manipulate single-electron quantum dots. We further observe large and widely tunable valley splittings, from 54 to 239 μeV. Tight-binding calculations, and the tunability of the valley splitting, indicate that these results can mainly be attributed to random concentration fluctuations that are amplified by the presence of Ge alloy in the heterostructure, as opposed to a deterministic enhancement due to the concentration oscillations. Quantitative predictions for several other heterostructures point to the Wiggle Well as a robust method for reliably enhancing the valley splitting in future qubit devices.

Date: 2022
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DOI: 10.1038/s41467-022-35510-z

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