Journal
PHYSICAL REVIEW B
Volume 104, Issue 8, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevB.104.085406
Keywords
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Funding
- Army Research Office (ARO) [W911NF-17-1-0274]
- Vannevar Bush Faculty Fellowship program by the Basic Research Office of the Assistant Secretary of Defense for Research and Engineering
- Office of Naval Research [N00014-15-10029]
- DOE [DE-FG02-03ER46028]
- NSF through the UW-Madison MRSEC [DMR-1720415]
- MRI program [DMR-1625348]
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Researchers successfully modified the Si/SiGe heterostructure by introducing a spike in germanium concentration, resulting in an increased valley splitting. Experimental evidence showed that the doubling effect of valley splitting was robust and nearly independent of external factors, laying a foundation for future heterostructure modifications.
Silicon-germanium heterostructures have successfully hosted quantum dot qubits, but the intrinsic near-degeneracy of the two lowest valley states poses an obstacle to high-fidelity quantum computing. We present a modification to the Si/SiGe heterostructure by the inclusion of a spike in germanium concentration within the quantum well in order to increase the valley splitting. The heterostructure is grown by chemical vapor deposition and magnetospectroscopy is performed on gate-defined quantum dots to measure the excited state spectrum. We demonstrate a large and widely tunable valley splitting as a function of applied vertical electric field and lateral dot confinement. We further investigate the role of the germanium spike by means of tight-binding simulations in single-electron dots and show a robust doubling of the valley splitting when the spike is present, as compared to a standard (spike-free) heterostructure. This doubling effect is nearly independent of the electric field, germanium content of the spike, and spike location. This experimental evidence of a stable, tunable quantum dot, despite a drastic change to the heterostructure, provides a foundation for future heterostructure modifications.
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