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Performance of SNSPDs at varying cooling conditions

M. Hofherr, Dagmar Rall, K. Ilin, Stefan Wünsch, Alexey Semenov, Heinz‐Wilhelm Hübers, M. Siegel

Published Oct 1, 2010• 0 citations
OpenAlex

Abstract

For superconducting nanowire single-photon detectors \n(SNSPD), there is a wide market of applications, like correlation spectroscopy or quantum cryptography, that profits from detectors with large speed and high detection efficiency. SNSPDs made of ultra-thin NbN films, patterned as a meander nanowire with a width in the range of 100 nm, offer a great change for the future to cover these specifications. NbN has been proven to be an excellent material for the development of SNSPD. \nIn context of high detection efficiency, a very low dark count rate is needed to satisfy the demands of several applications. Former studies show, that there is a certain relation between the detection mechanism and the dark counts [1], [2]. The origin of dark counts is due to thermal fluctuations in the meander structure of a SNSPD. To reduce this dark count rate, an investigation \nof influence of cooling conditions on the dark counts is \nnecessary.

Related papers

Improvement of SNSPD Detection Efficiency by Variation of NbN Chemical Composition

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•Oct 1, 2010•0 citations

Emerging materials for superconducting nanowire photon counting arrays

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Shigehito Miki, Taro Yamashita, Hirotaka Terai +3 more

We have developed a practical superconducting nanowire single photon detector (SNSPD) system with our superconducting thin films and devices fabrication, optical coupling packaging, and cryogenic technology. The SNSPD devices were fabricated from high-quality niobium nitride (NbN) ultra-thin films that were epitaxially grown on single-crystal MgO substrates, and optical cavity structure were applied for improvement of photo absorption efficiency. The SNSPD system was developed based on a compact Gifford-McMahon (GM) cryocooler, in which SNSPD can operate continuously at temperature of 2.9 K +/- 10 mK with low power consumption without any liquid cryogens. The system detection efficiencies at 1550 nm wavelength (at a 100 Hz dark count rate) were found to be 2.6% for device without optical cavity and 21% for device with optical cavity. The response speed of devices showed maximally 200 MHz with 5 × 5 mm square device, and timing jitter of 100 ps full width at a half maximum (FWHM) was observed.

IEEE International Conference on Space Optical Systems and Applications (ICSOS)•May 1, 2011•0 citations
For superconducting nanowire single-photon detectors \n(SNSPD), there is a wide market of applications, like correlation spectroscopy or quantum cryptography, that profits from detectors with large speed and high detection efficiency. SNSPDs made of ultra-thin NbN films, patterned as a meander nanowire with a width in the range of 100 nm, offer a great change for the future to cover these specifications. NbN has been proven to be an excellent material for the development of SNSPD. \nIn context of high detection efficiency, a very low dark count rate is needed to satisfy the demands of several applications. Former studies show, that there is a certain relation between the detection mechanism and the dark counts [1], [2]. The origin of dark counts is due to thermal fluctuations in the meander structure of a SNSPD. To reduce this dark count rate, an investigation \nof influence of cooling conditions on the dark counts is \nnecessary.
Ever since it has been shown that two-dimensionally constricted superconductors can be used to detect single photons, effort has been invested to optimize such devices for applications. In most cases, the detection efficiency, defining the ratio of counted photons vs. incoming photons and hence the sensitivity of the device, is the most important parameter. However, depending on the applications, other parameters, like the absolute pulse strength or the dark count rate, might be important to adjust. \nPrincipally, such a superconducting nanowire single photon detector (SNSPD) consists of a very thin superconducting film, which is patterned into a narrow meandering line. To tune the properties of such devices, the optimization of the geometry and layout of such structures has already been the topic of several investigations within our group [1], [2]. However, the device performance can also be influenced by changing the material properties of the superconducting thin film which provides the basis of the SNSPD.
Superconducting nanowire single-photon detectors (SNSPDs) are the leading technology for low noise, high efficiency infrared single-photon detection. The basic SNSPD consists of a nanowire patterned in an ultrathin superconducting thin film, which is cooled below its critical temperature and biased close to its critical current. The absorption of a single-photon creates a resistive region, triggering a fast output voltage pulse which can be readily amplified and registered. The excellent performance of SNSPDs at near-infrared and telecommunications wavelengths has led to their adoption in important applications such as quantum secure communications, single-photon spectroscopy and single-photon LIDAR. A clear challenge for the SNSPD community is to extend the spectral range of SNSPDs into the mid infrared, and to improve material uniformity to enable the realization of large area arrays for multimode or free space coupling. The aim of this work is to evaluate potential materials for next generation mid-infrared SNSPD arrays. In this work, thin films of polycrystalline NbN and amorphous MoSi have been optimized to test the uniformity of a multipixel array configuration composed of 8 nanowire meander structures covering 10 um x 10 um area, 100 nm width and 50% filling factor. The 8-pixels SNSPD arrays have been patterned on 8 nm thickness NbN grown on high resistivity silicon (HR Si) substrate at room temperature and at 800 °C exhibiting respectively 4.4 K and 7.3 K as mean critical temperature across the pixels. The 8- pixels SNSPD array patterned on 8 nm thickness MoSi cooling the HR Si substrate to -180 °C has exhibited a mean critical temperature of 3.2 K across the pixels. Optical properties have been measured by an attenuated 1550 nm laser diode source delivered by single mode optical fibre at a controlled distance from the chip in order to broadly illuminate the array. The optical properties have been studied only for the 8 nm thickness NbN SNSPD array grown at room temperature has demonstrated uniform optical properties across pixels exhibiting similar saturation of the internal efficiency over a large bias, similar dark count rate and similar timing jitter (about 137 ps) across pixels. In the single photon regime at 1550 nm, pixels 4 and 6 of the 8 nm thickness NbN SNSPD array exhibit 28.4% and 4.7% pixel detection efficiency as measured at the bias current 95% of their respective critical current at 2.2 K.
Nanoscopic superconducting meander patterns offer great promise as a new class of cryogenic radiation sensors capable of single photon detection. To realize this potential, control of the superconducting properties on the nanoscale is imperative. To this end, Superconducting Nanowire Single Photon Detectors (SNSPDs) are under development by means Energetic Neutral Atom Beam Lithography and Epitaxy, or ENABLE. ENABLE can growth highly-crystalline, epitaxial thin-film materials, like NbN, at low temperatures; such wide-ranging control of fabrication parameters is enabling the optimization of film properties for single photon detection. T{sub c}, H{sub c2}, {zeta}{sub GL} and J{sub c} of multiple thin films and devices have been studied as a function of growth conditions. The optimization of which has already produced devices with properties rivaling all reports in the existing literature.
The spectral detection efficiency and the dark count rate of superconducting nanowire single-photon detectors (SNSPD) have 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 decrease of the dark count rates more than two orders of magnitude 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.
Superconducting nanowire single photon detectors (SNSPD) have unique characteristics of ultra low dark counts and wide spectrum sensitivity. These natures are indispensable for the evaluation of ultra-broadband parametric fluorescence, which are used for the quantum optical coherence tomography and novel optical non-linear experiments. Here we report the spectral dependence of the detection efficiency of a meander type SNSPD device, having reduced strip width of 50 nm, over a wide spectrum range up to near infra-red wavelength. The fiber coupled, meander type device was fabricated using 6 nm thick Niobium nitride (NbN) nanowires of reduced strip width, 50 nm, patterned over a MgO substrate with active area of 10 x 10 μm2. A maximum efficiency of 32% at 500 nm, 30% at 600 nm, 16% at 800 nm, 10% at 1000 nm, and 1% at 1550 nm with the normalized bias current of 0.95 (bias 37 μA ) was observed at 4.2 K. The salient feature of the device is, it exhibits a very low dark count rate (DCR) of only 2 Hz at the standard operating bias of 37 μA and ultra low DCR of 0.01Hz at 34 μA. Moreover, at this reduced bias with 0.01Hz DCR, the detection efficiency is not appreciably decreased in the visible region (32% at 500 nm and 30% at 600 nm) and an order decrease is observed (0.1%) at 1550 nm. The noise equivalent power (NEP) is of the order 10-19 WHz-1/2 in the visible region and 10-17 WHz- 1/2 in the near IR region. Ultra-broad band parametric fluorescence of band width from 791 nm to 1610 nm generated by a quasi-phase matched (QPM) device was successfully detected with this SSPD.
We have developed a practical superconducting nanowire single photon detector (SNSPD) system with our superconducting thin films and devices fabrication, optical coupling packaging, and cryogenic technology. The SNSPD devices were fabricated from high-quality niobium nitride (NbN) ultra-thin films that were epitaxially grown on single-crystal MgO substrates, and optical cavity structure were applied for improvement of photo absorption efficiency. The SNSPD system was developed based on a compact Gifford-McMahon (GM) cryocooler, in which SNSPD can operate continuously at temperature of 2.9 K +/- 10 mK with low power consumption without any liquid cryogens. The system detection efficiencies at 1550 nm wavelength (at a 100 Hz dark count rate) were found to be 2.6% for device without optical cavity and 21% for device with optical cavity. The response speed of devices showed maximally 200 MHz with 5 × 5 mm square device, and timing jitter of 100 ps full width at a half maximum (FWHM) was observed.