posted on 2023-01-04, 18:35authored byCedric Corley-Wiciak, Carsten Richter, Marvin H. Zoellner, Ignatii Zaitsev, Costanza L. Manganelli, Edoardo Zatterin, Tobias U. Schülli, Agnieszka A. Corley-Wiciak, Jens Katzer, Felix Reichmann, Wolfgang M. Klesse, Nico W. Hendrickx, Amir Sammak, Menno Veldhorst, Giordano Scappucci, Michele Virgilio, Giovanni Capellini
A 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.