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arXiv:2210.15215 · Journal of Physics Communications

Single photon detection performance of highly disordered NbTiN thin films

Ruoyan Ma, Rui Shu, Xingyu Zhang, Aobo Yu, Jia Huang, You Xiao, Huiqin Yu, Xiaoyu Liu, Hao Li, Per Eklund, Xiaofu Zhang, Lixing You

Published May 1, 2023• 13 citations
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Abstract

Abstract We experimentally investigated the detection performance of highly disordered Nb x Ti 1 − x N based superconducting nanowire single photon detectors (SNSPDs). The dependence on the composition of the transition temperature T c for Nb x Ti 1 − x N films show a dome-like behavior on the Nb content, with a maximal T c at x Nb ∼ 0.65 , and the Nb 0.65 Ti 0.35 N films also combine relatively large sheet resistance and intermediate residual resistivity ratio. Moreover, 60-nm-wide and 7-nm-thick Nb 0.65 Ti 0.35 N nanowires show a switching current as high as 14.5 μ A, and saturated intrinsic detection efficiency with a plateau of more than 2 μ A at 2.4 K. Finally, the corresponding SNSPDs on an alternative SiO 2 /Ta 2 O 5 dielectric mirror showed a system detection efficiency of approximately 92% for 1550 nm photons, and the timing jitter is around 26 ps. Our results demonstrate that the highly disordered Nb x Ti 1 − x N

DOI
10.1088/2399-6528/acd747

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IEEE Globecom Workshops (GC Wkshps)•Dec 4, 2023•2 citations
Abstract We experimentally investigated the detection performance of highly disordered Nb x Ti 1 − x N based superconducting nanowire single photon detectors (SNSPDs). The dependence on the composition of the transition temperature T c for Nb x Ti 1 − x N films show a dome-like behavior on the Nb content, with a maximal T c at x Nb ∼ 0.65 , and the Nb 0.65 Ti 0.35 N films also combine relatively large sheet resistance and intermediate residual resistivity ratio. Moreover, 60-nm-wide and 7-nm-thick Nb 0.65 Ti 0.35 N nanowires show a switching current as high as 14.5 μ A, and saturated intrinsic detection efficiency with a plateau of more than 2 μ A at 2.4 K. Finally, the corresponding SNSPDs on an alternative SiO 2 /Ta 2 O 5 dielectric mirror showed a system detection efficiency of approximately 92% for 1550 nm photons, and the timing jitter is around 26 ps. Our results demonstrate that the highly disordered Nb x Ti 1 − x N
The intrinsic detection performance of superconducting nanowire single photon detectors (SNSPDs) is highly dependent on the superconducting properties of underlying thin films. This report outlines the enhancement of detection performance for single telecom wavelength photons in disordered NbTiN SNSPD at 4.2 K. By increasing the nitrogen content and deposition pressure, the NbTiN films show suppression in critical temperature and an increase in sheet resistance. Notably, the resulting SNSPDs display a broader saturation plateau at 2.2 K, leading to superior detection performance at 4.2 K. With the disordered 7-nm-thick NbTiN films, we fabricated SNSPDs with system detection efficiency up to 83% for 1550 nm photons at 4.2 K. Moreover, these devices also show saturated intrinsic detection efficiency for 2000 nm photons. With the features outlined, the devices can be integrated into the idle 4.2 K stage of the dilution refrigerator for applications in optical quantum information processing or utilize for detecting laser radar signals in airborne platforms.
Niobium Titanium nitride (NbTiN) based superconducting nanowire single photon detectors (SNSPDs) are known for their high performance across a wide spectral range, from the X-ray to the mid-infrared. Nonetheless, fabrication challenges and performance degradation attributable to surface oxidation and lack of uniformity in films thinner than 5 nm remain a significant barrier for achieving high-quality detectors. In this work, we study the influence of a Silicon capping layer on film properties and on the performance of SNSPDs. A Silicon capping layer effectively suppresses oxidation and increases the superconducting transition temperature. This enables superconductivity in films as thin as 3 nm at 3 K, increases critical current in patterned nanowires and significantly extends the saturation plateau from the visible to the near infrared (up to 2050 nm): These detectors maintain sub-50 ps timing jitter, even for nanowires as wide as 250 nm and with detection areas of 20x20μm2. Our results establish that thinner films protected by a capping layer allow for the fabrication of wider wires, decreasing nanofabrication challenges and extending the operating temperature range for efficient single photon detection.
Niobium titanium nitride-based superconducting nanowire single photon detectors (SNSPDs) are known for their high performance across a wide spectral range, from the x-ray to the mid-infrared. Nonetheless, fabrication challenges and performance degradation attributable to surface oxidation and lack of uniformity in films thinner than 5 nm remain a significant barrier for achieving high-quality detectors. In this work, we study the influence of a silicon capping layer on film properties and on the performance of SNSPDs. A silicon capping layer effectively suppresses oxidation and increases the superconducting transition temperature. This enables superconductivity in films as thin as 3 nm at 3 K, increases critical current in patterned nanowires, and significantly extends the saturation plateau from the visible to the near infrared (up to 2050 nm): These detectors maintain sub-50 ps timing jitter, even for nanowires as wide as 250 nm and with detection areas of 20 × 20μm2. Our results establish that thinner films protected by a capping layer allow for the fabrication of wider wires, decreasing nanofabrication challenges and extending the operating temperature range for efficient single photon detection.
N superconducting films and show that a Nb fraction of x = 0.62 allows for the fabrication of detectors from films as thick as 9 nm and covering an active area of 20 µm, with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm. This is a signature of an internal detection efficiency saturation, achieved while maintaining the high time resolution associated with NbTiN and operation at 2.5K. With our optimized recipe, we reliably fabricated detectors with high critical current densities reaching a saturation plateau at 1550 nm with 80% system detection efficiency and with a FWHM timing jitter as low as 19.5 ps.
Nbx_xx​Ti1−x_{1-x}1−x​N low timing jitter single-photon detectors with unity internal efficiency at 1550 nm and 2.5 K
The requirements in quantum optics experiments for high single photon detection efficiency, low timing jitter, low dark count rate and short dead time have been fulfilled with the development of superconducting nanowire single photon detectors. Although they offer a detection efficiency above 90%, achieving a high time resolution in devices made of amorphous materials is a challenge, particularly at temperatures above 0.8 K. Devices made from niobium nitride and niobium titanium nitride allow to reach the best timing jitter, but in turn have stronger requirements in terms of film quality to achieve a high efficiency. Here we take advantage of the flexibility of reactive co-sputter deposition to tailor the composition of NbxTi1-xN superconducting films, and show that a Nb fraction of x = 0.62 allows for the fabrication of detectors from films as thick as 9 nm and covering an active area of 20 μm, with a wide detection saturation plateau at telecom wavelengths and in particular at 1550 nm. This is a signature of an internal detection efficiency saturation, achieved while maintaining the high time resolution associated with NbTiN and operation at 2.5K. With our optimized recipe, we reliably fabricated detectors with high critical current densities reaching a saturation plateau at 1550 nm with 80% system detection efficiency, and with a FWHM timing jitter as low as 19.47 ps.
Superconducting nanowire single-photon detectors (SNSPDs) are a key building block for photonic quantum technologies, as they provide a means for efficient readout of optical circuits with low timing jitter, dark counts and dead time. In this contribution we give a general overview of the working principle of these devices and look into several engineering aspects. We discuss the influence of the stoichiometry of NbTiN thin-films on detector performance and find that a ratio of 65:35 Nb:Ti results in the highest saturation of SNSPDs fabricated from these films. Furthermore, we study the impact of helium ion irradiation on the efficiency of SNSPDs. We show that with this technique the efficiency of an SNSPD can be improved from below 1% to 42%. Finally, we discuss the impact of embedding the SNSPDs into an optical cavity on the system detection efficiency. By employing a half-cavity under the detector we are able to boost the efficiency from 30% to 50% for a detector with a fill factor of 0.33.