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Fluctuations and Dark Count Rates in Superconducting NbN Single-Photon Detectors

Andreas Engel 2,3Alexei Semenov 3Heinz-Wilhelm Hübers 3Konstantin S. Ilin 1Michael Siegel 1

1. Universität Karlsruhe, Karlsruhe 76128, Germany
2. Physics Institute of the University of Zurich, Winterthurerstr. 190, Zürich 8057, Switzerland
3. German Aerospace Center, Institute of Planetary Research (DLR Berlin), Rutherfordstr. 2, Berlin 12489, Germany


As the size of superconducting structures in one or more dimensions are more and more reduced fluctuations in the superconducting phase become increasingly important. These fluctuations lead to noise in thin-film or nano-structured detectors and ultimately limit their sensitivity. Fluctuating quasi-particle numbers and temporarily created vortex-antivortex pairs are two possible noise-sources near the superconducting phase transition. We considered thermodynamic fluctuations occurring with a probability proportional to exp(-ΔF/kBT), where ΔF is the change in free energy, kB the Boltzmann constant and T the temperature. ΔF itself is temperature and current dependent in a non-trivial way. We will present model calculations and compare the bias-current and temperature dependence with experimental dark count rates obtained for a NbN single-photon detector. The detector consisted of a thin and narrow meander, which was biased with a direct current slightly less than the temperature dependent critical current. Sufficiently large fluctuations caused voltage transients very similar to those caused by absorbed visible and near-infrared photons and are the major contribution to the measured dark count rates.


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Presentation: poster at E-MRS Fall Meeting 2004, Symposium E, by Andreas Engel
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-27 10:49
Revised:   2009-06-08 12:55