Smirnov, K., Korneev, A., Minaeva, O., Divochiy, A., Tarkhov, M., Ryabchun, S., et al. (2007). Ultrathin NbN film superconducting single-photon detector array. In J. Phys.: Conf. Ser. (Vol. 61, pp. 1081–1085).
Abstract: We report on the fabrication process of the 2 × 2 superconducting single-photon detector (SSPD) array. The SSPD array is made from ultrathin NbN film and is operated at liquid helium temperatures. Each detector is a nanowire-based structure patterned by electron beam lithography process. The advances in fabrication technology allowed us to produce highly uniform strips and preserve superconducting properties of the unpatterned film. SSPD exhibit up to 30% quantum efficiency in near infrared and up to 1% at 5-μm wavelength. Due to 120 MHz counting rate and 18 ps jitter, the time-domain multiplexing read-out is proposed for large scale SSPD arrays. Single-pixel SSPD has already found a practical application in non-invasive testing of semiconductor very-large scale integrated circuits. The SSPD significantly outperformed traditional single-photon counting avalanche diodes.
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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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Korneev, A., Divochiy, A., Tarkhov, M., Minaeva, O., Seleznev, V., Kaurova, N., et al. (2008). New advanced generation of superconducting NbN-nanowire single-photon detectors capable of photon number resolving. In J. Phys.: Conf. Ser. (Vol. 97, 012307 (1 to 6)).
Abstract: We present our latest generation of ultrafast superconducting NbN single-photon detectors (SSPD) capable of photon-number resolving (PNR). We have developed, fabricated and tested a multi-sectional design of NbN nanowire structures. The novel SSPD structures consist of several meander sections connected in parallel, each having a resistor connected in series. The novel SSPDs combine 10 μm × 10 μm active areas with a low kinetic inductance and PNR capability. That resulted in a significantly reduced photoresponse pulse duration, allowing for GHz counting rates. The detector's response magnitude is directly proportional to the number of incident photons, which makes this feature easy to use. We present experimental data on the performances of the PNR SSPDs. The PNR SSPDs are perfectly suited for fibreless free-space telecommunications, as well as for ultrafast quantum cryptography and quantum computing.
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Verevkin, A. A., Ptitsina, N. G., Chulcova, G. M., Gol'Tsman, G. N., Gershenzon, E. M., & Yngvesson, K. S. (1996). Determination of the limiting mobility of a two-dimensional electron gas in AlxGa1-xAs/GaAs heterostructures and direct measurement of the energy relaxation time. Phys. Rev. B Condens. Matter., 53(12), R7592–R7595.
Abstract: We present results for a method to measure directly the energy relaxation time (τe) for electrons in a single AlxGa1−xAs/GaAs heterojunction; measurements were performed from 1.6 to 15 K under quasiequilibrium conditions. We find τeαT−1 below 4 K, and τe independent of T above 4 K. We have also measured the energy-loss rate, ⟨Q⟩, by the Shubnikov-de Haas technique, and find ⟨Q⟩α(T3e−T3) for T<~4.2 K; Te is the electron temperature. The values and temperature dependence of τe and ⟨Q⟩ for T<4 K agree with calculations based on piezoelectric and deformation potential acoustic phonon scattering. At 4.2 K, we can also estimate the momentum relaxation time, τm, from our measured τe. This leads to a preliminary estimate of the phonon-limited mobility at 4.2 K of μ=3×107 cm2/Vs (ns=4.2×1011 cm−2), which agrees well with published numerical calculations, as well as with an earlier indirect estimate based on measurements on a sample with much higher mobility.
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Lusche, R., Semenov, A., Korneeva, Y., Trifonov, A., Korneev, A., Gol'tsman, G., et al. (2014). Effect of magnetic field on the photon detection in thin superconducting meander structures. Phys. Rev. B, 89(10), 104513 (1 to 7).
Abstract: We have studied the influence of an externally applied magnetic field on the photon and dark count rates of meander-type niobium nitride superconducting nanowire single-photon detectors. Measurements have been performed at a temperature of 4.2 K, and magnetic fields up to 250 mT have been applied perpendicularly to the meander plane. While photon count rates are field independent at weak applied fields, they show a strong dependence at fields starting from approximately ±25 mT. This behavior, as well as the magnetic field dependence of the dark count rates, is in good agreement with the recent theoretical model of vortex-assisted photon detection and spontaneous vortex crossing in narrow superconducting lines. However, the local reduction of the superconducting free energy due to photon absorption, which is the fitting parameter in the model, increases much slower with the photon energy than the model predicts. Furthermore, changes in the free-energy during photon counts and dark counts depend differently on the current that flows through the meander. This indicates that photon counts and dark counts occur in different parts of the meander.
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