Enhancing intrinsic detection efficiency of superconducting nanowire single-photon detectors via helium ion irradiation

TL;DR

This paper demonstrates a post-processing helium ion irradiation technique to nearly double the intrinsic detection efficiency of NbN superconducting nanowire single-photon detectors at near-infrared wavelengths, significantly improving their performance.

Contribution

The authors introduce a novel helium ion irradiation method to enhance the intrinsic detection efficiency of SNSPDs without affecting optical absorptance.

Findings

Intrinsic detection efficiency increased from 49% to 92%.

Superconducting energy gap was reduced by ion irradiation.

Optical absorptance remained unchanged.

Abstract

Realizing an NbN superconducting nanowire single-photon detector (SNSPD) with a 100% intrinsic detection efficiency (IDE) at the near-infrared wavelengths is still challenging. Herein, we developed a post-processing method to increase the IDE of NbN SNSPDs to near unity using a 20 keV helium ion irradiation. The IDE enhancement was achieved owing to the ion-induced reduction of the superconducting energy gap and the electron density of states at the Fermi level, determined with the electrical and magnetic transport measurements. The change in optical absorptance of the irradiated SNSPD was negligible as confirmed by the measured optical reflectance and system detection efficiency (SDE). Benefited with the IDE enhancement, the SDE of an irradiated device was significantly increased from 49% to 92% at 2.2 K for a 1550 nm wavelength.