Nuclear Spin-Depleted, Isotopically Enriched 70 Ge/ 28 Si 70 Ge Quantum Wells.

The p-symmetry of the hole wavefunction is associated with a weaker hyperfine interaction, which makes hole spin qubits attractive candidates for quantum processors. However, recent studies demonstrated that hole qubits are still very sensitive to nuclear spin bath, thus highlighting the need for nuclear spin-free Ge qubits to suppress this decoherence channel. Herein, this work demonstrates the epitaxial growth of 73 Ge-depleted isotopically enriched 70 Ge/SiGe quantum wells. The growth was achieved by reduced pressure chemical vapor deposition using isotopically purified monogermane 70 GeH 4 and monosilane 28 SiH 4 with an isotopic purity higher than 99.9 % and 99.99 %, respectively. The quantum wells consist of a series of 70 Ge/SiGe heterostructures grown on Si wafers using a Ge virtual substrate and a graded SiGe buffer layer. The isotopic purity is investigated using atom probe tomography following an analytical procedure addressing the discrepancies in the isotopic content caused by the overlap of isotope peaks in mass spectra. The nuclear spin background in the quantum wells was found to be sensitive to the growth conditions. The lowest concentration of nuclear spin-full isotopes 73 Ge and 29 Si in the heterostructure was established at 0.01 % in the Ge quantum well and SiGe barriers. The measured average distance between nuclear spins reaches 3-4 nm in 70 Ge/ 28 Si 70 Ge, which is an order of magnitude larger than in natural Ge/SiGe heterostructures. This article is protected by copyright. All rights reserved.