Buried Unstrained Germanium Channels
A Lattice-Matched Platform for Quantum Technology
Davide Costa (Kavli institute of nanoscience Delft, TU Delft - QCD/Scappucci Lab, TU Delft - QuTech Advanced Research Centre)
Patrick Del Vecchio (TU Delft - QuTech Advanced Research Centre, Kavli institute of nanoscience Delft, TU Delft - QCD/Bosco Group)
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 - BUS/Quantum Delft, TU Delft - QuTech Advanced Research Centre)
Alberto Tosato (TU Delft - QuTech Advanced Research Centre, TU Delft - BUS/Quantum Delft, Kavli institute of nanoscience Delft)
Davide Degli Esposti (Kavli institute of nanoscience Delft, TU Delft - QCD/Vandersypen Lab)
Vladimir Calvi (TU Delft - QuTech Advanced Research Centre, TU Delft - QCD/Scappucci Lab, Kavli institute of nanoscience Delft)
Luca Moreschini (Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre, 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 (TU Delft - QCD/Bosco Group, Kavli institute of nanoscience Delft, TU Delft - QuTech Advanced Research Centre)
Giordano Scappucci (TU Delft - QuTech Advanced Research Centre, TU Delft - Electrical Engineering, Mathematics and Computer Science, Kavli institute of nanoscience Delft, TU Delft - QCD/Scappucci Lab)
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Abstract
Strained germanium (๐-Ge) and strained silicon (๐-Si) buried quantum wells have enabled advanced spin-qubit quantum processors. However, in the absence of suitable lattice-matched substrates, ๐-Ge and ๐-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 (๐-SiGe) barrier, eliminating the need for metamorphic buffers altogether. In a structure with a 52-nm-thick ๐-SiGe barrier, a low-disorder two-dimensional hole gas is demonstrated with a high-mobility of 1.33 ร105 cm2/Vs and a low percolation density of 1.4โข(1) ร1010 cmโ2. 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 ๐-factor, pointing to a significant heavy-holeโlight-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 ๐-factor in Ge than in ๐-Ge. The prospects of strong spinโorbit interaction, isotopic purification, and of hosting superconducting pairing correlations make this platform appealing for fast quantum hardware and hybrid quantum systems.
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