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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Large-area NbN superconducting nanowire avalanche photon detectors with saturated detection efficiency

Ryan P. Murphy, Matthew E. Grein, Theodore Gudmundsen, Adam N. McCaughan, Faraz Najafi, Karl K. Berggren, Francesco Marsili, Eric A. Dauler

Published May 13, 2015• 0 citations
Publisher

Abstract

Superconducting circuits comprising SNSPDs placed in parallel—superconducting nanowire avalanche photodetectors, or SNAPs—have previously been demonstrated to improve the output signal-to-noise ratio (SNR) by increasing the critical current. In this work, we employ a 2-SNAP superconducting circuit with narrow (40 nm) niobium nitride (NbN) nanowires to improve the system detection efficiency to near-IR photons while maintaining high SNR. Additionally, while previous 2-SNAP demonstrations have added external choke inductance to stabilize the avalanching photocurrent, we show that the external inductance can be entirely folded into the active area by cascading 2-SNAP devices in series to produce a greatly increased active area. We fabricated series-2-SNAP (s2-SNAP) circuits with a nanowire length of 20 μm with cascades of 2-SNAPs providing the choke inductance necessary for SNAP operation. We observed that (1) the detection efficiency saturated at high bias currents, and (2) the 40 nm 2-SNAP circuit critical current was approximately twice that for a 40 nm non-SNAP configuration.

DOI
10.1117/12.2178322

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Superconducting circuits comprising SNSPDs placed in parallel—superconducting nanowire avalanche photodetectors, or SNAPs—have previously been demonstrated to improve the output signal-to-noise ratio (SNR) by increasing the critical current. In this work, we employ a 2-SNAP superconducting circuit with narrow (40 nm) niobium nitride (NbN) nanowires to improve the system detection efficiency to near-IR photons while maintaining high SNR. Additionally, while previous 2-SNAP demonstrations have added external choke inductance to stabilize the avalanching photocurrent, we show that the external inductance can be entirely folded into the active area by cascading 2-SNAP devices in series to produce a greatly increased active area. We fabricated series-2-SNAP (s2-SNAP) circuits with a nanowire length of 20 μm with cascades of 2-SNAPs providing the choke inductance necessary for SNAP operation. We observed that (1) the detection efficiency saturated at high bias currents, and (2) the 40 nm 2-SNAP circuit critical current was approximately twice that for a 40 nm non-SNAP configuration.
We propose a novel design of superconducting nanowire avalanche photodetectors (SNAPs), which combines the advantages of multistage avalanche SNAPs to lower the avalanche current IAVand that of series-SNAPs to reduce the reset time. As proof of principle, we fabricated 800 devices with large detection area (15 μm × 15 μm) and five different designs on a single silicon chip for comparison, which include standard SNSPDs, series-3-SNAPs, and our modified series-SNAPs with double-stage avalanche structure 2*2-SNAPs, 2*3-SNAPs, and 3*3-SNAPs. The former three types of the detectors demonstrate fully saturated device detection efficiencies of ~20% while the latter two types are latching at larger bias currents. In addition, the IAVof 2*2-SNAPs is only 64% of the switching current ISWthat is lower than series-3-SNAPs (74%) and well below that of 4-SNAPs (84%) reported elsewhere. We also measure that the exponential decay times of the detectors are proportional to 1/ n2due to the lack of external choke inductors. In particular, the decay time of 3*3-SNAPs is only 0.89 ns compared to the standard SNSPDs' 63.2 ns, showing the potential to attain GHz counting rates.
Superconducting nanowire single-photon detectors (SNSPDs) with both an ultra-large-active area and a high count rate (CR) are challenging from the design and fabrication. Here, we develop a NbN SNSPD with a circular active area of 300 μm-in-diameter and use multiple approaches to boost the maximal count rate (MCR). This large-active-area SNSPD is divided into nine pixels (parts). Each pixel consists of serially connected two superconducting nanowire avalanche photodetectors (SC-2SNAP), which yielded a four-fold reduction in the kinetic inductance of a single pixel. To further increase MCR, an optimized series resistance of about 380 Ω is added to each pixel, reducing the full recovery time of each pixel from a few microseconds to approximately 90 ns. All nine pixels show uniform superconducting critical temperatures of ∼7.4 K and switching currents in the range of 15.3–16.7 μA. When the detector coupled to a single-mode fiber and illuminated with 1064-nm photons, the single-pixel exhibits a well-saturated system detection efficiency (SDE) of 67% at a dark CR of 30 Hz, and its CR exceeds 10 MHz with an SDE of 50%. When coupled to a 200-μm multi-mode fiber, the total SDE of nine pixels is approximately 42% and the total MCR exceeds 43 MHz.
Recent progress in the development of superconducting nanowire single photon detectors (SSPD or SNSPD) has delivered excellent performance, and has had a great impact on a range of research fields. Significant efforts are being made to further improve the technology, and a primary concern remains to resolve the trade-offs between detection efficiency (DE), timing jitter, and response speed. We present a stable and high-performance fiber-coupled niobium titanium nitride superconducting nanowire avalanche photon detector (SNAP) that resolves these trade-offs. Autocorrelation function measurement revealed an afterpulse-free operation in serially connected two SNAP (SC-2SNAP), even in the absence of a choke inductor, achieving a 7.65 times faster response speed than standard SSPDs. The SC-2SNAP device showed a system detection efficiency (SDE) of 81.0% with wide bias current margin, a dark count rate of 6.8 counts/s, and full width at half maximum timing jitter of 68 ps, operating in a practical Gifford-McMahon cryocooler system.
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.
Superconducting devices offer the potential to perform at speeds and detection efficiencies higher than what is possible using conventional technologies (such as semiconducting avalanche photodiodes and photomultiplier tubs) for wavelengths from the ultraviolet to the mid-infrared. As a result, there has been increasing interest in using superconducting optical photon detectors in a variety of applications. There has been significant progress in using these types of detectors in areas of basic research such as quantum information science and quantum optics. These applications require detectors that have extremely low dark count rates, high count rates, and high quantum efficiency. I will begin by describing some of our earlier work on superconducting Transition-Edge Sensor (TES). In particular, I will describe some of the engineering involved in the cryogenic, electrical, and optical packaging so that these devices can be easily coupled into fiber-based optics. I will also describe our recent work on developing superconducting nanowire single photon detectors (SNSPD or SSPD). An SNSPD is an ultra-thin, ultra-narrow (nm scale) superconducting meander that is current biased just below its critical current density. When one or more photon is absorbed, a hot spot is formed that causes the superconductor to develop a resistance and consequently a voltage pulse. At NIST and JPL, we have been developing nanowire detectors using an amorphous alloy of tungsten-silicide. We will describe to construct systems using tungsten-silicide nanowires to achieve high detection efficiency (>90% at 1550nm). I will also describe our work to improve the performance of the device by fabricating multiple nanowires in an electrically parallel structure to implement a superconducting nanowire avalanche photodiode (SNAP)[1]. One example of this type of detector is shown in Fig 1. In this case, there are two tungsten silicide layers separated by a dielectric layer to optimize detection of light for any polarization[2]. In addition, progress on other types of SNAP detectors will be described to increase the signal size from a single photon, reduce the recovery time of the device, and to improve the jitter.