Germanium quantum well Josephson field effect transistors and interferometers

TL;DR

This paper demonstrates the fabrication and characterization of germanium-based hybrid superconductor-semiconductor devices, including Josephson transistors and SQUIDs, showing gate-controlled supercurrent and insights into material interfaces for quantum applications.

Contribution

It introduces Ge/SiGe quantum-well heterostructures with aluminum contacts for hybrid devices, highlighting their supercurrent control and interface properties, advancing quantum device technology.

Findings

Gate-controlled supercurrent in Ge channels up to 1 micrometer

Induced superconducting gap measured via tunnel spectroscopy

Ge diffusion into aluminum contacts observed

Abstract

Hybrid superconductor-semiconductor structures attract increasing attention owing to a variety of potential applications in quantum computing devices. They can serve to the realization of topological superconducting systems, as well as gate-tunable superconducting quantum bits. Here we combine a SiGe/Ge/SiGe quantum-well heterostructure hosting high-mobility two-dimensional holes and aluminum superconducting leads to realize prototypical hybrid devices, such as Josephson field-effect transistors (JoFETs) and superconducting quantum interference devices (SQUIDs). We observe gate-controlled supercurrent transport with Ge channels as long as one micrometer and estimate the induced superconducting gap from tunnel spectroscopy measurements in superconducting point-contact devices. Transmission electron microscopy reveals the diffusion of Ge into the aluminum contacts, whereas no aluminum is detected in the Ge channel.