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- ItemNanoscale Mapping of the 3D Strain Tensor in a Germanium Quantum Well Hosting a Functional Spin Qubit Device(Washington, DC : Soc., 2023) Corley-Wiciak, Cedric; Richter, Carsten; Zoellner, Marvin H.; Zaitsev, Ignatii; Manganelli, Costanza L.; Zatterin, Edoardo; Schülli, Tobias U.; Corley-Wiciak, Agnieszka A.; Katzer, Jens; Reichmann, Felix; Klesse, Wolfgang M.; Hendrickx, Nico W.; Sammak, Amir; Veldhorst, Menno; Scappucci, Giordano; Virgilio, Michele; Capellini, GiovanniA strained Ge quantum well, grown on a SiGe/Si virtual substrate and hosting two electrostatically defined hole spin qubits, is nondestructively investigated by synchrotron-based scanning X-ray diffraction microscopy to determine all its Bravais lattice parameters. This allows rendering the three-dimensional spatial dependence of the six strain tensor components with a lateral resolution of approximately 50 nm. Two different spatial scales governing the strain field fluctuations in proximity of the qubits are observed at <100 nm and >1 μm, respectively. The short-ranged fluctuations have a typical bandwidth of 2 × 10-4 and can be quantitatively linked to the compressive stressing action of the metal electrodes defining the qubits. By finite element mechanical simulations, it is estimated that this strain fluctuation is increased up to 6 × 10-4 at cryogenic temperature. The longer-ranged fluctuations are of the 10-3 order and are associated with misfit dislocations in the plastically relaxed virtual substrate. From this, energy variations of the light and heavy-hole energy maxima of the order of several 100 μeV and 1 meV are calculated for electrodes and dislocations, respectively. These insights over material-related inhomogeneities may feed into further modeling for optimization and design of large-scale quantum processors manufactured using the mainstream Si-based microelectronics technology.
- ItemIntersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells(Basel : MDPI, 2020) Persichetti, Luca; Montanari, Michele; Ciano, Chiara; Di Gaspare, Luciana; Ortolani, Michele; Baldassarre, Leonetta; Zoellner, Marvin; Mukherjee, Samik; Moutanabbir, Oussama; Capellini, Giovanni; Virgilio, Michele; De Seta, Monican-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemRaman shifts in MBE-grown SixGe1 − x − ySny alloys with large Si content(Chichester [u.a.] : Wiley, 2021) Schlipf, Jon; Tetzner, Henriette; Spirito, Davide; Manganelli, Costanza L.; Capellini, Giovanni; Huang, Michael R. S.; Koch, Christoph T.; Clausen, Caterina J.; Elsayed, Ahmed; Oehme, Michael; Chiussi, Stefano; Schulze, Jörg; Fischer, Inga A.We examine the Raman shift in silicon–germanium–tin alloys with high silicon content grown on a germanium virtual substrate by molecular beam epitaxy. The Raman shifts of the three most prominent modes, Si–Si, Si–Ge, and Ge–Ge, are measured and compared with results in previous literature. We analyze and fit the dependence of the three modes on the composition and strain of the semiconductor alloys. We also demonstrate the calculation of the composition and strain of SixGe1 − x − ySny from the Raman shifts alone, based on the fitted relationships. Our analysis extends previous results to samples lattice matched on Ge and with higher Si content than in prior comprehensive Raman analyses, thus making Raman measurements as a local, fast, and nondestructive characterization technique accessible for a wider compositional range of these ternary alloys for silicon-based photonic and microelectronic devices.
- ItemShallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology(Weinheim : Wiley-VCH, 2019) Sammak, Amir; Sabbagh, Diego; Hendrickx, Nico W.; Lodari, Mario; Wuetz, Brian Paquelet; Tosato, Alberto; Yeoh, LaReine; Bollani, Monica; Virgilio, Michele; Schubert, Markus Andreas; Zaumseil, Peter; Capellini, Giovanni; Veldhorst, Menno; Scappucci, GiordanoBuried-channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 10 5 cm 2 V −1 s −1 ) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top-gate of a dopant-less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 10 11 cm −2 , light effective mass (0.09m e ), and high effective g-factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim