Buried Unstrained Germanium Channels
A Lattice-Matched Platform for Quantum Technology
Davide Costa (TU Delft - QCD/Scappucci Lab, TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft)
Patrick Del Vecchio (Kavli institute of nanoscience Delft, TU Delft - QCD/Bosco Group, TU Delft - QuTech Advanced Research Centre)
Karina Hudson (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Scappucci Lab)
Lucas E.A. Stehouwer (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - BUS/Quantum Delft)
Alberto Tosato (TU Delft - BUS/Quantum Delft, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
Davide Degli Esposti (TU Delft - QCD/Vandersypen Lab, Kavli institute of nanoscience Delft)
Vladimir Calvi (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Scappucci Lab)
Luca Moreschini (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/Scappucci Lab)
Mario Lodari (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Scappucci Lab, Kavli institute of nanoscience Delft)
Stefano Bosco (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Bosco Group)
Giordano Scappucci (Kavli institute of nanoscience Delft, TU Delft - Electrical Engineering, Mathematics and Computer Science, TU Delft - QCD/Scappucci Lab, TU Delft - QuTech Advanced Research Centre)
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Abstract
Strained germanium ((Formula presented.) -Ge) and strained silicon ((Formula presented.) -Si) buried quantum wells have enabled advanced spin-qubit quantum processors. However, in the absence of suitable lattice-matched substrates, (Formula presented.) -Ge and (Formula presented.) -Si are deposited on defective, metamorphic SiGe buffers, which may impact device performance and scaling. Here an alternative platform is introduced based on the heterojunction between bulk unstrained Ge and a lattice-matched strained silicon-germanium ((Formula presented.) -SiGe) barrier, eliminating the need for metamorphic buffers altogether. In a structure with a 52-nm-thick (Formula presented.) -SiGe barrier, a low-disorder two-dimensional hole gas is demonstrated with a high-mobility of (Formula presented.) and a low percolation density of (Formula presented.). Quantum transport shows that holes confined in the buried unstrained Ge channel have a strong density-dependent in-plane effective mass and out-of-plane (Formula presented.) -factor, pointing to a significant heavy-hole–light-hole mixing in agreement with theory. Measurements of Zeeman-split levels in quantum point contacts further highlight this character, showing a two-fold larger in-plane (Formula presented.) -factor in Ge than in (Formula presented.) -Ge. The prospects of strong spin–orbit interaction, isotopic purification, and of hosting superconducting pairing correlations make this platform appealing for fast quantum hardware and hybrid quantum systems.