Origin of giant valley splitting in silicon quantum wells induced by superlattice barriers

Abstract

Enhancing valley splitting in SiGe heterostructures is a crucial task for developing silicon spin qubits. Complex SiGe heterostructures, sharing a common feature of four-monolayer (4ML) Ge layer next to the silicon quantum well (QW), have been computationally designed to have giant valley splitting approaching 9 meV. However, none of them has been fabricated may due to their complexity. Here, we remarkably simplify the original designed complex SiGe heterostructures by laying out the Si QW directly on the Ge substrate followed by capping a (Ge4Si4)n superlattice(SL) barrier with a small sacrifice on VS as it is reduced from a maximum of 8.7 meV to 5.2 meV. Even the smallest number of periods (n = 1) will also give a sizable VS of 1.6 meV, which is large enough for developing stable spin qubits. We also develop an effective Hamiltonian model to reveal the underlying microscopic physics of enhanced valley splitting by (Ge4Si4)n SL barriers. We find that the presence of the SL barrier will reduce the VS instead of enhancing it. Only the (Ge4Si4)n SL barriers with an extremely strong coupling with Si QW valley states provide a remarkable enhancement in VS. These findings lay a solid theoretical foundation for the realization of sufficiently large VS for Si qubits.

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Cited by in corpus (6)

• SiGe quantum wells with oscillating Ge concentrations for quantum dot qubits
• Practical Strategies for Enhancing the Valley Splitting in Si/SiGe Quantum Wells
• Low disorder and high valley splitting in silicon
• Utilizing multimodal microscopy to reconstruct Si/SiGe interfacial atomic disorder and infer its impacts on qubit variability
• Atomistic compositional details and their importance for spin qubits in isotope-purified silicon-germanium quantum wells
• Valley splitting by extended zone effective mass approximation incorporating strain in silicon