Author(s): Wang, G (Wang, Gang); Song, ZG (Song, Zhi-Gang); Luo, JW (Luo, Jun-Wei); Li, SS (Li, Shu-Shen)

Source: PHYSICAL REVIEW B Volume: 105 Issue: 16 Article Number: 165308 DOI: 10.1103/PhysRevB.105.165308 Published: APR 21 2022

Abstract: Enhancing valley splitting in SiGe heterostructures is crucial for developing silicon spin qubits. Complex SiGe heterostructures, sharing a common feature of four-monolayer (4 ML) Ge layer next immediately to the silicon quantum well (QW), have been computationally designed in 2013 to have giant valley splitting approaching 9 meV and hence could be used to overcome the challenge of valley splitting towards the experimental realization of Si quantum computing. However, none of them has been successfully fabricated, perhaps due to their complexity. Here, we remarkably simplify the originally designed complex SiGe heterostructures by laying out the Si QW directly on the SiGe substrate followed by capping a (Ge4Si4)n superlattice (SL) barrier with a sacrifice in valley splitting (VS), which is reduced from a maximum value of 8.7 to 5.2 meV. Even the smallest number of SL periods (n = 1) will also give a sizable VS of 1.6 meV, which is large enough for developing stable spin qubits. We further develop an effective Hamiltonian model to reveal the physical mechanism underlying the enhanced valley splitting by the (Ge4Si4)n SL barriers. We surprisingly find that the presence of the SL barrier will reduce rather than enhance the VS in most cases. The only exception is the (Ge4Si4)n SL barriers, where their miniband states have such a strong coupling with Si QW valley states that they provide an even larger VS. These findings lay a solid theoretical foundation for overcoming the valley splitting issue of SiGe heterostructures in the experiment that is heading toward Si quantum computing.

Accession Number: WOS:000804798200002

Author Identifiers:

Author        Web of Science ResearcherID        ORCID Number

Wang, Gang                  0000-0001-6958-3484

ISSN: 2469-9950

eISSN: 2469-9969

Full Text: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.165308