Regensburg 2025 – wissenschaftliches Programm
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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur
KFM 5: Instrumentation, Microscopy and Tomography with X-ray Photons, Electrons, Ions and Positrons
KFM 5.2: Vortrag
Montag, 17. März 2025, 15:15–15:30, H9
Single-phase valence band structure of a Ge0.85Si0.15 Crystal - Insights by momentum microscopy — •Andreas Fuhrberg1, Pia M. Düring1, Kevin Gradwohl2, Olena Fedchenko3, Yaryna Lytvynenko3, Olena Tkach3, Sergii Chernov4, Christoph Schlueter4, Gerd Schönhense3, Hans-Joachim Elmers3, and Martina Müller1 — 1Universität Konstanz — 2IKZ, Berlin — 3Universität Mainz — 4DESY, Hamburg
Spin qubits are the fundamental components of quantum computing devices. Planar Ge/Ge1−xSix heterostructure qubits have proven to be advantageous for upscaling and fabrication. The Si concentration of the Ge1−xSix buffer has been shown to be an important parameter for tuning the valence band (VB) electronic structure of Ge/Ge1−xSix qubits by homoepitaxial strain, which is difficult to realize experimentally without phase separation.
Synchrotron-based hard X-ray momentum microscopy (MM) is used to study the VB electronic structure of a Ge0.85Si0.15 single crystal grown to provide well-defined small strain. Our MM experiments reveal an individual VB structure of Ge0.85Si0.15, that is clearly distinct from Si and Ge references. The shape of the heavy/light hole band and split-off band follows that of Ge, but with lower binding energies at Γ, X and L points and a reduced split-off band gap, hence no evidence for phase separation. Additional diffraction experiments, supported by Bloch wave calculations, show that the Si atoms occupy Ge lattice positions within the crystal. This result is very promising for the future experimental realization of single-phase GeSi-based spin qubits.
Keywords: Ge-Qubits; GeSi; Valence band; X-ray momentum microscopy