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Casaburi, A., Ejrnaes, M., Quaranta, O., Gaggero, A., Mattioli, F., Leoni, R., et al. (2008). Experimental characterization of NbN nanowire optical detectors with parallel stripline configuration. In J. Phys.: Conf. Ser. (Vol. 97, 012265 (1 to 6)). IOP Publishing.
Abstract: We have developed a novel geometrical configuration for NbN-based superconducting single photon optical detector (SSPD) that achieves two goals: a much lower intrinsic impedance, and a consequently greater bandwidth, and a much larger signal amplitude compared to the standard meandered configuration. This has been obtained by implementing a properly designed parallel stripline structure where a cascade switching mechanism occurs when one of the striplines is hit by an optical photon. The overall switching occurs synchronously and in a very short time, giving rise to a strong and fast voltage pulse. The SSPD have been realized using state of the art NbN deposition technology and e-beam lithography. The strips are 100 nm wide and 5 μm long and have been realized with 4 nm NbN film on sapphire and Si substrate. We report on experimental characterization of such novel devices. The performances of the proposed novel type of SSPD are compared with standard SSPD design and results in terms of signal amplitude, risetime and effective detection area.
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Gol’tsman, G., Okunev, O., Chulkova, G., Lipatov, A., Dzardanov, A., Smirnov, K., et al. (2001). Fabrication and properties of an ultrafast NbN hot-electron single-photon detector. IEEE Trans. Appl. Supercond., 11(1), 574–577.
Abstract: A new type of ultra-high-speed single-photon counter for visible and near-infrared wavebands based on an ultrathin NbN hot-electron photodetector (HEP) has been developed. The detector consists of a very narrow superconducting stripe, biased close to its critical current. An incoming photon absorbed by the stripe produces a resistive hotspot and causes an increase in the film’s supercurrent density above the critical value, leading to temporary formation of a resistive barrier across the device and an easily measurable voltage pulse. Our NbN HEP is an ultrafast (estimated response time is 30 ps; registered time, due to apparatus limitations, is 150 ps), frequency unselective device with very large intrinsic gain and negligible dark counts. We have observed sequences of output pulses, interpreted as single-photon events for very weak laser beams with wavelengths ranging from 0.5 /spl mu/m to 2.1 /spl mu/m and the signal-to-noise ratio of about 30 dB.
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Yang, J. K. W., Dauler, E., Ferri, A., Pearlman, A., Verevkin, A., Gol’tsman, G., et al. (2005). Fabrication development for nanowire GHz-counting-rate single-photon detectors. IEEE Trans. Appl. Supercond., 15(2), 626–630.
Abstract: We have developed a fabrication process for GHz-counting-rate, single-photon, high-detection-efficiency, NbN, nanowire detectors. We have demonstrated two processes for the device patterning, one based on the standard polymethylmethacrylate (PMMA) organic positive-tone electron-beam resist, and the other based on the newer hydrogen silsesquioxane (HSQ) negative-tone spin-on-glass resist. The HSQ-based process is simple and robust, providing high resolution and the prospect of high fill-factors. Initial testing results show superconductivity in the films, and suggest that the devices exhibit photosensitivity.
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Gol’tsman, G. N., Smirnov, K., Kouminov, P., Voronov, B., Kaurova, N., Drakinsky, V., et al. (2003). Fabrication of nanostructured superconducting single-photon detectors. IEEE Trans. Appl. Supercond., 13(2), 192–195.
Abstract: Fabrication of NbN superconducting single-photon detectors, based on the hotspot effect is presented. The hotspot formation arises in an ultrathin and submicrometer-width superconductor stripe and, together with the supercurrent redistribution, leads to the resistive detector response upon absorption of a photon. The detector has a meander structure to maximally increase its active area and reach the highest detection efficiency. Main processing steps, leading to efficient devices, sensitive in 0.4-5 /spl mu/m wavelength range, are presented. The impact of various processing steps on the performance and operational parameters of our detectors is discussed.
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de Lara, D. P., Ejrnaes, M., Casaburi, A., Lisitskiy, M., Cristiano, R., Pagano, S., et al. (2008). Feasibility investigation of NbN nanowires as detector in time-of-flight mass spectrometers for macromolecules of interest in biology (proteins). J. Low Temp. Phys., 151(3-4), 771–776.
Abstract: We are investigating the possibility of using NbN nanowires as detectors in time-of-flight mass spectrometers for investigation of macromolecules of interest in biology (proteins). NbN nanowires could overcome the two major drawbacks encountered so far by cryogenic detectors, namely the low working temperature in the mK region and the slow temporal response. In fact, NbN nanowires can work at 5 K and the response time is at least a factor 10–100 better than that of other cryogenic detectors. We present a feasibility study based on a numerical code to calculate the response of a NbN nanowire. The parameter space is investigated at different energies from IR to macromolecules (i.e. from eV to keV) in order to understand if larger value of film thickness and width can be used for the keV energy region. We also present preliminary experimental results of irradiation with X-ray photons of NbN to simulate the effect of macromolecules of the same energy.
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