Atomistic Compositional Details and Their Importance for Spin Qubits in Isotope‐Purified Silicon Quantum Wells

Advanced Science, vol. 11, pp. e2407442

Abstract

Abstract Understanding crystal characteristics down to the atomistic level increasingly emerges as a crucial insight for creating solid state platforms for qubits with reproducible and homogeneous properties. Here, isotope concentration depth profiles in a SiGe/ 28 Si/SiGe heterostructure are analyzed with atom probe tomography (APT) and time‐of‐flight secondary‐ion mass spectrometry down to their respective limits of isotope concentrations and depth resolution. Spin‐echo dephasing times and valley energy splittings E VS around have been observed for single spin qubits in this quantum well (QW) heterostructure, pointing toward the suppression of qubit decoherence through hyperfine interaction with crystal host nuclear spins or via scattering between valley states. The concentration of nuclear spin‐carrying 29 Si is 50 ± 20ppm in the 28 Si QW. The resolution limits of APT allow to uncover that both the SiGe/ 28 Si and the 28 Si/SiGe interfaces of the QW are shaped by epitaxial growth front segregation signatures on a few monolayer scale. A subsequent thermal treatment, representative of the thermal budget experienced by the heterostructure during qubit device processing, broadens the top SiGe/ 28 Si QW interface by about two monolayers, while the width of the bottom 28 Si/SiGe interface remains unchanged. Using a tight‐binding model including SiGe alloy disorder, these experimental results suggest that the combination of the slightly thermally broadened top interface and of a minimal Ge concentration of % in the QW, resulting from segregation, is instrumental for the observed large . Minimal Ge additions <1%, which get more likely in thin QWs, will hence support high E VS without compromising coherence times. At the same time, taking thermal treatments during device processing as well as the occurrence of crystal growth characteristics into account seems important for the design of reproducible qubit properties.

Authors 12

1. Jan Klos Aachen

   Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

   Affiliation as printed

   JARA‐FIT Institute for Quantum Information Forschungszentrum Jülich GmbH & RWTH Aachen University 52074 Aachen Germany

2. Jan Tröger

   University of Münster

   Affiliation as printed

   Institute of Materials Physics University of Münster 48149 Münster Germany

   Tascon GmbH 48149 Münster Germany

3. Jens Keutgen Aachen I. Physikalisches Institut IA

   RWTH Aachen University

   Affiliation as printed

   I. Physikalisches Institut IA RWTH Aachen University 52074 Aachen Germany

4. Merritt P. Losert

   University of Wisconsin–Madison

   Affiliation as printed

   University of Wisconsin‐Madison Madison WI 53706 USA

5. Nikolay V. Abrosimov

   Leibniz Institute for Crystal Growth

   Affiliation as printed

   Leibniz‐Institut für Kristallzüchtung (IKZ) 12485 Berlin Germany

6. Joachim Knoch Aachen Institute of Semiconductor Electronics

   RWTH Aachen University

   Affiliation as printed

   Institute of Semiconductor Electronics RWTH Aachen University 52074 Aachen Germany

7. Hartmut A. Bracht

   University of Münster

   Affiliation as printed

   Institute of Materials Physics University of Münster 48149 Münster Germany

8. S. N. Coppersmith

   UNSW Sydney

   Affiliation as printed

   University of New South Wales Sydney 2025 Australia

9. Mark G. Friesen

   University of Wisconsin–Madison

   Affiliation as printed

   University of Wisconsin‐Madison Madison WI 53706 USA

10. Oana Cojocaru‐Mirédin corresponding Aachen I. Physikalisches Institut IA

    University of Freiburg · RWTH Aachen University

    Affiliation as printed

    I. Physikalisches Institut IA RWTH Aachen University 52074 Aachen Germany

    INATECH, Albert‐Ludwigs Universität Freiburg 79110 Freiburg im Breisgau Germany

11. Lars R. Schreiber corresponding Aachen

    Forschungszentrum Jülich · Jülich Aachen Research Alliance · RWTH Aachen University

    Affiliation as printed

    ARQUE Systems GmbH 52074 Aachen Germany

    JARA‐FIT Institute for Quantum Information Forschungszentrum Jülich GmbH & RWTH Aachen University 52074 Aachen Germany

12. Dominique Bougeard corresponding

    University of Regensburg

    Affiliation as printed

    Institut für Experimentelle und Angewandte Physik Universität Regensburg 93040 Regensburg Germany