Superconducting Proximity Effect in Planar Germanium

The co-integration of spin, superconducting and topological systems is emerging as an exciting pathway for scalable and high fidelity quantum information technology. Planar germanium is a front-runner semiconductor for building quantum processors with spin-qubits, but the lack of a high quality interface with a superconductor has slowed progress with hybrid superconducting-semiconducting devices. Here we take this step and demonstrate a high quality, oxide-free interface between high-mobility planar germanium and a superconducting germanosilicide contact. Electrical characterization reveals near-unity transparency in Josephson junctions, ballistic superconductivity, hard induced superconducting gap in quantum point contacts, phase control over a Josephson junctions in a SQUID device, and a superconductor to insulator transition in gated two-dimensional semiconductor–superconductor array. These results expand the quantum technology toolbox in germanium and provide new avenues for exploring monolithic superconductor-semiconductor quantum circuits towards scalable quantum information.