Fast-Recovery Epitaxial NbN Superconducting Nanowire Single-Photon Detectors with Saturated Efficiency at 1550 nm in Liquid Helium

TL;DR

This paper demonstrates that epitaxial NbN films on sapphire enable superconducting nanowire single-photon detectors with high efficiency and fast response at 1550 nm in liquid helium, advancing quantum photonics technology.

Contribution

It introduces epitaxial NbN films on sapphire for SNSPDs, achieving high efficiency and rapid reset times simultaneously, with detailed characterization and modeling of the underlying mechanisms.

Findings

High internal efficiency saturated at 1550 nm

Short reset times achieved at 4.2 K

Epitaxial growth preserves film quality and enhances performance

Abstract

Achieving both high internal efficiency and fast reset times at elevated temperatures remains challenging due to limited understanding of how film properties govern SNSPD performance. We demonstrate that epitaxial NbN films on sapphire enable simultaneous high efficiency and rapid response. We fabricate and characterize SNSPDs based on these films deposited via DC magnetron sputtering on c-cut sapphire. High-quality epitaxial growth preserves a low electron diffusion coefficient and promotes strong electron-phonon coupling, yielding a high critical temperature and efficient hotspot formation in the dirty limit. X-ray diffraction and transmission electron microscopy confirm epitaxial alignment and lattice order. Nanowires of 20 nm width exhibit saturated internal efficiency at 1550 nm wavelength and short reset times at 4.2 K, enabled by lattice matching and high thermal conductance of the sapphire interface. Ab initio modeling reproduces photon count rates, linking device performance quantitatively to film properties such as diffusivity and electron-phonon coupling.