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arXiv:1205.4290 · Optics Express

Reduced dark counts in optimized geometries for superconducting nanowire single photon detectors

Mohsen K. Akhlaghi, Haig A. Atikian, Amin Eftekharian, Marko Lončar, A. Hamed Majedi

Published Oct 1, 2012• 49 citations
arXivHTMLPDF

Abstract

We have experimentally compared the critical current, dark count rate and photo-response of 100nm wide superconducting nanowires with different bend designs. Enhanced critical current for nanowires with optimally rounded bends, and thus with no current crowding, are observed. Furthermore, we find that the optimally designed bend significantly reduces the dark counts without compromising the photo-response of the device. The results can lead to major improvements in superconducting nanowire single photon detectors.

DOI
10.1364/oe.20.023610

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We have experimentally compared the critical current, dark count rate and photo-response of 100nm wide superconducting nanowires with different bend designs. Enhanced critical current for nanowires with optimally rounded bends, and thus with no current crowding, are observed. Furthermore, we find that the optimally designed bend significantly reduces the dark counts without compromising the photo-response of the device. The results can lead to major improvements in superconducting nanowire single photon detectors.
Abstract Current crowding at bends of superconducting nanowire single-photon detector (SNSPD) is one of the main factors limiting the performance of meander-style detectors with large filling factors. In this paper, we propose a new concept to reduce the influence of the current crowding effect, a so-called variable thickness SNSPD, which is composed of two regions with different thicknesses. A larger thickness of bends in comparison to the thickness of straight nanowire sections locally reduces the current density and reduces the suppression of the critical current caused by current crowding. This allows variable thickness SNSPD to have a higher critical current, an improved detection efficiency, and decreased dark count rate in comparison with a standard uniform thickness SNSPD with an identical geometry and film quality.
Detecting single photons is essential for applications such as dark matter detection, quantum science and technology, and biomedical imaging. Superconducting nanowire single-photon detectors (SNSPDs) excel in this task due to their near-unity detection efficiency, subhertz dark count rates, and picosecond timing jitter. However, a local increase of current density (current crowding) in the bends of meander-shaped SNSPDs limits these performance metrics. By locally irradiating the SNSPD’s straight segments with helium ions while leaving the bends unirradiated, we realize current crowding–free SNSPDs with simultaneously enhanced sensitivity: After irradiation with 800 ions nm −2 , locally irradiated SNSPDs showed a relative saturation plateau width of 37%, while fully irradiated SNSPDs reached only 10%. This larger relative plateau width allows operation at lower relative bias currents, thereby reducing the dark count rate while still detecting single photons efficiently. We achieve an internal detection efficiency of 94% with 7 mHz dark count rate near the onset of saturating detection efficiency for a wavelength of 780 nm.
In this paper, we theoretically show that a multi-layer superconducting nanowire single-photon detector (SNSPD) is capable of approaching characteristics of an ideal SNSPD in terms of the quantum efficiency, dark count, and band-width. A multi-layer structure improves the performance in two ways. First, the potential barrier for thermally activated vortex crossing, which is the major source of dark counts and the reduction of the critical current in SNSPDs is elevated. In a multi-layer SNSPD, a vortex is made of 2D-pancake vortices that form a stack. It will be shown that the stack of pancake vortices effectively experiences a larger potential barrier compared to a vortex in a single-layer SNSPD. This leads to an increase in the experimental critical current as well as significant decrease in the dark count rate. In consequence, an increase in the quantum efficiency for photons of the same energy or an increase in the sensitivity to photons of lower energy is achieved. Second, a multi-layer structure improves the efficiency of single-photon absorption by increasing the effective optical thickness without compromising the single-photon sensitivity.
Nanowire superconducting single-photon detectors (SSPDs) consist of a superconducting wire of nanoscale cross-section [1], typically 4×100 nm2. A current close to the device critical current renders the nanowire sensitive to single photons. SSPDs are known for their high efficiency, low jitter, low dark count rate and fast reset time. An important challenge for future application of SSPDs is to extend the useful wavelength range towards the infrared without comprising detector speed or dark count rate. To this end, we explore optical designs with wider nanowires that utilize efficient detection of single photons at the edge of the nanowire. Silicon nanowires on top of a NbN nanowire increase both the calculated total absorption and the internal detection efficiency significantly compared to a standard meandering wire geometry.
Emerging quantum technologies and weak-light applications demand photon detectors with a simultaneously high counting rate and near-unity efficiency. Superconducting nanowire single-photon detectors can achieve >90% system detection efficiency, but maintaining this efficiency at high counting rates remains challenging. Although parallel-configured superconducting nanowire avalanche photodetectors (SNAPs) reduce the recovery time, their designs intensify the current crowding effects at bends, leading to persistent challenges in achieving high system detection efficiency. We developed an optimized bend structure for meandered parallel nanowires called staggered bends, which increased the switching current by 11.3% in the 2-SNAPs. At 1064 nm, the optimized 2-SNAP and 3-SNAP with staggered bends achieved system detection efficiencies of 96.6% and 98.1%, respectively. Meanwhile, these devices maintain 90% system detection efficiency while achieving counting rates of 3.1 MHz and 10.3 MHz. This study establishes a practical framework for SNAPs with demonstrated performance metrics that could enable advancements in the frontiers of quantum information.
© 2021 IOP Publishing Ltd. Current crowding at bends of superconducting nanowire single-photon detector (SNSPD) is one of the main factors limiting the performance of meander-style detectors with large filling factors. In this paper, we propose a new concept to reduce the influence of the current crowding effect, a so-called variable thickness SNSPD, which is composed of two regions with different thicknesses. A larger thickness of bends in comparison to the thickness of straight nanowire sections locally reduces the current density and reduces the suppression of the critical current caused by current crowding. This allows variable thickness SNSPD to have a higher critical current, an improved detection efficiency, and decreased dark count rate in comparison with a standard uniform thickness SNSPD with an identical geometry and film quality.