Broadening of hot-spot response spectrum of superconducting NbN nanowire single-photon detector with reduced nitrogen content

TL;DR

This study demonstrates that reducing nitrogen content in NbN films enhances superconducting nanowire single-photon detectors by decreasing dark counts and extending spectral response, due to improved film uniformity and critical current ratios.

Contribution

It introduces a method to optimize NbN SNSPDs for infrared detection by adjusting nitrogen content to improve film uniformity and performance.

Findings

Dark count rates decreased by over two orders of magnitude.

Hot-spot response spectrum shifted to longer wavelengths.

Improved film uniformity correlated with better detector performance.

Abstract

The spectral detection efficiency and the dark count rate of superconducting nanowire single-photon detectors (SNSPD) has been studied systematically on detectors made from thin NbN films with different chemical compositions. Reduction of the nitrogen content in the 4 nm thick NbN films results in a more than two orders of magnitude decrease of the dark count rates and in a red shift of the cut-off wavelength of the hot-spot SNSPD response. The observed phenomena are explained by an improvement of uniformity of NbN films that has been confirmed by a decrease of resistivity and an increase of the ratio of the measured critical current to the depairing current. The latter factor is considered as the most crucial for both the cut-off wavelength and the dark count rates of SNSPD. Based on our results we propose a set of criteria for material properties to optimize SNSPD in the infrared spectral region.