Engineering Ge Profiles in Si/SiGe Heterostructures for Increased Valley Splitting
Lucas E.A. Stehouwer (TU Delft - QCD/Scappucci Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Merrit P. Losert (University of Wisconsin-Madison)
Maia Rigot (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QN/Greplová Lab)
Davide Degli Esposti (TU Delft - QCD/Vandersypen Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Sara Martí-Sánchez (Universitat Autònoma de Barcelona)
Maximillian Rimbach-Russ (Kavli institute of nanoscience Delft, TU Delft - QCD/Rimbach-Russ, TU Delft - QuTech Advanced Research Centre)
Jordi Arbiol (Universitat Autònoma de Barcelona)
Mark Friesen (University of Wisconsin-Madison)
Giordano Scappucci (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Scappucci Lab, TU Delft - Quantum Circuit Architectures and Technology, Kavli institute of nanoscience Delft)
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Abstract
Electron-spin qubits in Si/SiGe quantum wells are limited by the small and variable energy separation of the conduction-band valleys. While sharp quantum-well interfaces are pursued to increase the valley-splitting energy deterministically, here we explore an alternative approach to enhancing the valley splitting on average. We grow increasingly thinner quantum wells with broad interfaces to controllably increase the electron wave function overlap with Ge atoms. Quantum Hall measurements of two-dimensional electron gases reveal a linear correlation between valley splitting and disorder-induced single-particle energy-level broadening, driven by increasing alloy scattering at the Si/SiGe interface. We demonstrate enhanced valley splitting while maintaining respectable electron mobility, indicating a low-disorder electrostatic potential environment. Simulations using experimental Ge concentration profiles predict an average valley splitting in quantum dots that matches the enhancement observed in two-dimensional systems. Our results motivate the experimental realization of quantum-dot spin qubits in these heterostructures.
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