Soft X-Ray Single-Photon Detection With Superconducting Tantalum Nitride and Niobium Nanowires

Inderbitzin, K.; Engel, A.; Schilling, Andreas

doi:10.1109/tasc.2012.2234496

Cited by 17 publications

(18 citation statements)

References 18 publications

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“…SSPDs can also be used in the keV regime, either for detecting x-ray photons [36] or for detecting ions. The experiment by Suzuki et al [14] on ion detection in 800 nm wide, 10 nm thick, detectors has clearly demonstrated that the normal-core hot spot model is correct in the keV range.…”

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confidence: 99%

Experimental Test of Theories of the Detection Mechanism in a Nanowire Superconducting Single Photon Detector

et al. 2014

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We report an experimental test of the photodetection mechanism in a nanowire superconducting single photon detector. Detector tomography allows us to explore the 0.8-8 eV energy range via multiphoton excitations. High accuracy results enable a detailed comparison of the experimental data with theories for the mechanism of photon detection. We show that the temperature dependence of the efficiency of the superconducting single photon detector is determined not by the critical current but by the current associated with vortex unbinding. We find that both quasiparticle diffusion and vortices play a role in the detection event. DOI: 10.1103/PhysRevLett.112.117604 PACS numbers: 79.20.Ws, 03.65.Wj, 85.25.Oj Nanowire superconducting single photon detectors (SSPDs or SNSPDs) [1,2] are currently the most promising detection systems in the infrared, achieving detection efficiencies of up to 93% at 1550 nm [3]. Despite these technological advances, the fundamentals of the working principle of these detectors are poorly understood and under active investigation, both theoretically [4][5][6][7][8][9][10][11] and experimentally [12][13][14][15][16][17][18][19][20][21][22].A typical SSPD consists of a few nm thin film of a superconducting material such as NbN or WSi, nanofabricated into a meandering wire geometry. When biased sufficiently close to the critical current of the superconductor, the energy of one or several photons can be enough to trigger a local transition to the resistive state, resulting in a detection event. The energy of the absorbed photon is distributed through an avalanchelike process, creating a nonequlibrium population of quasiparticles. This quasiparticle population then disrupts the supercurrent flow, resulting eventually in a detection event.In this Letter, we address the nature of this disruption, which lies at the heart of the photodetection mechanism in SSPDs. At present, there are three important open questions. First, it is unknown whether the detection event occurs when the energy of the incident photon causes a cylindrical volume inside the wire to transition to the normal state [see Fig. 1(a)] [1], or whether it is enough for the superconductivity to be weakened but not destroyed by the depletion of Cooper pairs over a more extended region [see Fig. 1The second open question is whether magnetic vortices play any role in the detection mechanism. There are two varieties of vortex-based models. The first is an extension of the normal-core model, where, a vortex-antivortex pair forms at the point where the photon is absorbed [ Fig. 1(c)] [5]. In the second, the weakening of superconductivity lowers the energy barrier for either a vortex crossing [6,23] or a vortex-antivortex pair crossing [ Fig. 1(d)].The last open question pertains to the temperature dependence of the photoresponse of SSPDs. Intuitively, one would expect the SSPD to be less efficient at lower temperatures, as the detector works by breaking superconductivity and the energy gap of a superconductor decreases with increasing temp...

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Experimental Test of Theories of the Detection Mechanism in a Nanowire Superconducting Single Photon Detector

et al. 2014

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“…2 Variations of these detectors have also been used to detect higher energy particles, such as high kinetic-energy molecules in mass spectrometry, 3,4 or x-ray photons with keV-energies. 5,6 The active element of these detectors consists of a typically square meander of a superconducting NbN film of a few nanometer thickness. 7 Recently, alternative superconducting materials have been suggested, such as NbTiN, 8 TaN, 9 or WSi, 10 which may be better suited than NbN for certain applications.…”

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Numerical analysis of detection-mechanism models of superconducting nanowire single-photon detector

Engel

Schilling

2013

Journal of Applied Physics

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The microscopic mechanism of photon detection in superconducting nanowire single-photon detectors is still under debate. We present a simple but powerful theoretical model that allows us to identify essential differences between competing detection mechanisms. The model is based on quasi-particle multiplication and diffusion after the absorption of a photon. We then use the calculated spatial and temporal evolution of this quasi-particle cloud to determine detection criteria of three distinct detection mechanisms, based on the formation of a normal conducting spot, the reduction of the effective depairing critical current below the bias current, and a vortex-crossing scenario, respectively. All our calculations as well as a comparison to experimental data strongly support the vortex-crossing detection mechanism by which vortices and antivortices enter the superconducting strip from the edges and subsequently traverse it thereby triggering the detectable normal conducting domain. These results may therefore help to reveal the microscopic mechanism responsible for the detection of photons in superconducting nanowires. V C 2013 AIP Publishing LLC.

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“…We recently fabricated thick film superconducting nanowire single X-ray photon detectors (X-SNSPDs) based on Nb and TaN. 12,13 The area of these detectors is around several thousand square micrometers, and the dead time is as low as several nanoseconds. Hence the resulting maximum CPSPSM can be as high as 10 11 cps, nearly two orders of magnitude higher than the demands from clinical X-ray CT scanner, which would make this type of detectors excellently suitable for a CT application.…”

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“…The slope of the count rate as a function of the X-ray source current indicates that the detector works in the single-photon detection regime. 12,13 Figure 3 shows the count rates as functions of the bias current, normalized by the critical current at each temperature, for VA = 30 kV and 49.9 kV. The X-ray source current Ix has been fixed at 1 mA throughout the experiments.…”

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“…For comparison, in Nb and TaN based X-SNSPD, the calculated hotspot size is ~ 420 nm at 1.75 K and ~ 540 nm at 1.85 K, respectively. 12,13 Thus, the WSi materials are indeed more sensitive to photons with the same energy, and in order to improve the signal to noise ratio, we could in principle even further increase the nanowire width. Taking the X-ray photon flux into consideration, the system detection efficiency of the WSi detector is estimated to be 7.5%.…”

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Superconducting single X-ray photon detector based on W0.8Si0.2

2016

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We fabricated a superconducting single X-ray photon detector based on W0.8Si0.2, and we characterized its basic detection performance for keV-photons at different temperatures. The detector has a critical temperature of 4.97 K, and it is able to be operated up to 4.8 K, just below the critical temperature. The detector starts to react to X-ray photons at relatively low bias currents, less than 1% of Ic at T = 1.8 K, and it shows a saturated count rate dependence on bias current at all temperatures, indicating that the optimum internal quantum efficiency can always be reached. Dark counts are negligible up to the highest investigated bias currents (99% of Ic) and operating temperature (4.8 K). The latching effect affects the detector performance at all temperatures due to the fast recovery of the bias current; however, further modifications of the device geometry are expected to reduce the tendency for latching.Ultrafast single photon sensitive X-ray detectors have a potential for important applications in many areas. Using photoncounting detectors (PCDs), the image quality of the medical X-ray computed tomography (CT) with low X-ray dose can be significantly improved. 1, 2 Such applications can even be extended to single molecular, virus, or cell CT and X-ray imaging. 3The currently used energy integrating detectors (EIDs) in CT scanners and X-ray systems, however, have certain limits with regard to this technology. The EIDs measure the energy integrated signals of X-ray photons, 1, 4 and they are affected by the electronic noise and Swank noise. 5 As a result, the weight of low energy photons is decreased, which in turn leads to an increase of noise and a decrease of contrast. 1 Moreover, the performance of PCDs based on semiconductor technology is not impeccable as the respective count rate is limited. 1, 4, 6-7 These detectors have a typical dead time of several hundred nanoseconds, which limits the maximum count rate per pixel to a few megahertz. Meanwhile, the pixel size of these detectors is of the order of several hundred micrometers, which results in a maximum counts-per-second-per-square-millimeters (CPSPSM) of 10 6 cps. 1 The required count rate for a clinical X-ray CT scanner, however, may be as high as 10 9 cps. 6 Apart from the medical applications, ultrafast single X-ray photon detector can also be used in synchrotron X-ray sources, freeelectron lasers, and astronomy. Synchrotron radiation, for example, has provided the possibility to perform X-ray experiments at very short time scales, and the use of time resolving detectors is therefore essential. [8][9][10] The currently used a zhang@physik.uzh.ch

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Soft X-Ray Single-Photon Detection With Superconducting Tantalum Nitride and Niobium Nanowires

Cited by 17 publications

References 18 publications

Experimental Test of Theories of the Detection Mechanism in a Nanowire Superconducting Single Photon Detector

Experimental Test of Theories of the Detection Mechanism in a Nanowire Superconducting Single Photon Detector

Numerical analysis of detection-mechanism models of superconducting nanowire single-photon detector

Superconducting single X-ray photon detector based on W0.8Si0.2

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