Solid-State Reactions at Niobium-Germanium Interfaces in Hybrid Superconductor-Semiconductor Devices

TL;DR

This study investigates the solid-state reactions at niobium-germanium interfaces in hybrid superconductor-semiconductor devices, emphasizing low-temperature fabrication to preserve interface quality for quantum computing applications.

Contribution

It provides systematic analysis of Nb/Ge interfaces at cryogenic temperatures, highlighting the importance of low-temperature growth to minimize interdiffusion and optimize device performance.

Findings

Low-temperature Nb evaporation creates atomically abrupt interfaces.

Higher annealing temperatures cause Ge out-diffusion and interface degradation.

Minimizing chemical intermixing improves superconducting device performance.

Abstract

Hybrid Superconductor-Semiconductor (S-Sm) materials systems are promising candidates for quantum computing applications. Their integration into superconducting electronics has enabled on-demand voltage tunability at millikelvin temperatures. Ge quantum wells (Ge QWs) have been among the semiconducting platforms interfaced with superconducting Al to realize voltage tunable Josephson junctions. Here, we explore Nb as a superconducting material in direct contact with Ge channels by focusing on the solid-state reactions at the Nb/Ge interfaces. We employ Nb evaporation at cryogenic temperatures (100 K) to establish a baseline structure with atomically and chemically abrupt Nb/Ge interfaces. By conducting systematic photoelectron spectroscopy and transport measurements on Nb/Ge samples across varying annealing temperatures, we elucidated the influence of Ge out-diffusion on the ultimate performance of superconducting electronics. This study underlines the need for low-temperature growth to minimize chemical intermixing and band bending at the Nb/Ge interfaces.