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Spectral performance of a single-photon detector

A. Semenov, Andreas Engel, Heinz‐Wilhelm Hübers, Konstantin Il ́in, M. Siegel

Published Jan 1, 2005• 6 citations
OpenAlex

Abstract

We have experimentally studied the supercurrent-assisted formation of the resistive state in nano-structured disordered superconducting Nb(N) films after absorption of a single optical to near-infrared photon. The efficiency of the resistive state formation has a pronounced spectral cut-off; corresponding threshold photon energy decreases with the bias current. Analysis of the experimental data in the framework of the refined hot-spot model suggests that the quantum yield for near-infrared photons increases with the photon energy. Relaxation of the resistive state depends on the photon energy making the phenomena feasible for the development of energy resolving single-photon detectors.

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We have experimentally studied the supercurrent-assisted formation of the resistive state in nano-structured disordered superconducting Nb(N) films after absorption of a single optical to near-infrared photon. The efficiency of the resistive state formation has a pronounced spectral cut-off; corresponding threshold photon energy decreases with the bias current. Analysis of the experimental data in the framework of the refined hot-spot model suggests that the quantum yield for near-infrared photons increases with the photon energy. Relaxation of the resistive state depends on the photon energy making the phenomena feasible for the development of energy resolving single-photon detectors.
Single photon detectors based on meanders from 5-nm thin B1 niobium nitride nanostrips show moderate spectral resolution along with the spectral cut-off of the quantum efficiency occurring in the near-infrared spectral range. Beyond the cut-off there is a gradual decrease of the quantum efficiency. To describe the response beyond the cut-off we combine the previously developed hot-spot detection mechanism with the photon-induced unbinding of the vortex-antivortex pairs, which appear in the superconducting film below the Kosterlitz-Thouless phase transition. The detector responds to the absorption of a single photon with a voltage pulse whose amplitude depends on the photon energy. We report the observation of a photon-energy dependent statistical distribution of the pulse amplitude that defines the energy resolution of the detector. We analyzed the detector response to continuous and femtosecond-pulse radiation using broadband microwave amplifiers and a fast single-shot oscilloscope as well as integrating SQUID amplifiers. Our analysis suggests that both the amplitude and the duration of the response pulses are jointly controlled via the kinetic inductance of the meander line and the Joule power dissipated in the meander by the bias current.
Thin film cryogenic bolometers are widely used as integrating detectors for infrared and millimeter wave radiation. A superconducting quantum detector based on a nanometer-scaled structure may be an alternative for future applications where energy resolved single-photon detection and fast response times are simultaneously required. The mechanism responsible for the single-photon detection capability is due to the combined action of a hot-spot formation after photon absorption and a subsequent normal domain caused by an applied bias current [1]. We present recent results on energy resolution and spectral sensitivity of infrared quantum detectors made of different materials (Nb and NbN). The spectral response of the detector exhibits a pronounced threshold at a particular photon energy E0 that depends on the material and detector geometry. According to the detector model, information about the photons energy is contained in the amplitude and duration of the voltage pulse. A reasonable energy resolution is expected only for photon energies E >> E0. Preliminary experiments performed near the threshold energy have shown that the time integral of the response pulses indeed varied with the photon energy. The observed energy resolution of about 20% at 0.6 eV was not sufficient for practical applications. However, these preliminary data validate the response mechanism and support the envisaged performance at higher photon energies. [1] Semenov A D, Gol'tsman G N and Korneev A A 2001 Physica C 351 349.
We analyze the spectral performance of recently developed single-photon quantum detector that consists of a narrow, nanometer sized meander-line made from ultra-thin superconducting film. The detector exploits a combined detection mechanism, in which avalanche multiplication of quasiparticles after absorption of a single photon and the bias current jointly produce a normal domain that results in a voltage pulse developing between the meander ends. With either the wavelength increase or the bias current decrease, the single-photon detection regime exhibits a cut-off. The wavelength, at which the cut-off occurs, varies from infrared waves to visible light depending on the superconducting material and operation conditions. Structural and geometrical non-uniformities of the meander line smooth out the otherwise expected sharp drop of the detection efficiency beyond the cut-off. We refine the early detector model and propose a tentative explanation of how superconducting fluctuations may additionally extend the detection efficiency beyond the cut-off wavelength.
We report an experimental investigation of the hot-spot evolution in superconducting single-photon detectors made of disordered superconducting materials with different diffusivity and energy downconversion time values, i.e., 33-nm-thick NbN and 23-nm-thick NbC films. We have demonstrated that, in NbC film, only 405-nm photons produce sufficiently large hot spot to trigger a single-photon response. The dependence of detection efficiency on bias current for 405-nm photons in NbC is similar to that for 3400-nm photons in NbN. In NbC, large diffusivity and downconversion time result in 1-D critical current suppression profile compared with the usual 2-D profile in NbN.
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.