Verevkin, A. A., Ptitsina, N. G., Chulcova, G. M., Gol'tsman, G. N., Gershenzon, E. M., & Yngvesson, K. S. (1996). Direct measurements of energy relaxation time of electrons in AlGaAs/GaAs heterostructures under quasi-equilibrium conditions. Surface Science, 361-362, 569–573.
Abstract: For the first time, results are presented of a direct measurement of the energy relaxation time τε of 2D electrons in an AlGaAs/GaAs heterojunction at T = 1 and 5–20 K. A weak temperature dependence of τε for the T > 4K range and a linear temperature dependence of the reciprocal of τε for T < 4K have been observed. The linear dependence τε−1 ≈ T in the Bloch-Gruneisen regime is direct evidence of the predominance of the piezo-electric mechanism of electron-phonon interaction in non-elastic electron scattering processes. The values of τε in this regime are in very good agreement with the results of the Karpus theory. At higher temperatures, where the deformation-potential scattering becomes noticeable, a substantial disagreement between the experimental data and the theoretical results is observed.
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Lipatov, A., Okunev, O., Smirnov, K., Chulkova, G., Korneev, A., Kouminov, P., et al. (2002). An ultrafast NbN hot-electron single-photon detector for electronic applications. Supercond. Sci. Technol., 15(12), 1689–1692.
Abstract: We present the latest generation of our superconducting single-photon detector (SPD), which can work from ultraviolet to mid-infrared optical radiation wavelengths. The detector combines a high speed of operation and low jitter with high quantum efficiency (QE) and very low dark count level. The technology enhancement allows us to produce ultrathin (3.5 nm thick) structures that demonstrate QE hundreds of times better, at 1.55 μm, than previous 10 nm thick SPDs. The best, 10 × 10 μm2, SPDs demonstrate QE up to 5% at 1.55 μm and up to 11% at 0.86 μm. The intrinsic detector QE, normalized to the film absorption coefficient, reaches 100% at bias currents above 0.9 Ic for photons with wavelengths shorter than 1.3 μm.
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Il'in, K. S., Verevkin, A. A., Gol'tsman, G. N., & Sobolewski, R. (1999). Infrared hot-electron NbN superconducting photodetectors for imaging applications. Supercond. Sci. Technol., 12(11), 755–758.
Abstract: We report an effective quantum efficiency of 340, responsivity >200 A W-1 (>104 V W-1) and response time of 27±5 ps at temperatures close to the superconducting transition for NbN superconducting hot-electron photodetectors (HEPs) in the near-infrared and optical ranges. Our studies were performed on a few nm thick NbN films deposited on sapphire substrates and patterned into µm-size multibridge detector structures, incorporated into a coplanar transmission line. The time-resolved photoresponse was studied by means of subpicosecond electro-optic sampling with 100 fs wide laser pulses. The quantum efficiency and responsivity studies of our photodetectors were conducted using an amplitude-modulated infrared beam, fibre-optically coupled to the device. The observed picosecond response time and the very high efficiency and sensitivity of the NbN HEPs make them an excellent choice for infrared imaging photodetectors and input optical-to-electrical transducers for superconducting digital circuits.
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Shangina, E. L., Smirnov, K. V., Morozov, D. V., Kovalyuk, V. V., Goltsman, G. N., Verevkin, A. A., et al. (2011). Concentration dependence of energy relaxation time in AlGaAs/GaAs heterojunctions: direct measurements. Semicond. Sci. Technol., 26(2), 025013.
Abstract: We present measurements of the energy relaxation time, τε, of electrons in a single heterojunction in a quasi-equilibrium state using microwave time-resolved spectroscopy at 4.2 K. We find the relaxation time has a power-law dependence on the carrier density of the two-dimensional electron gas, τε∝nγs with γ = 0.40 ± 0.02 for values of the carrier density, ns, from 1.6 × 1011 to 6.6 × 1011cm−2. The results are in good agreement with predictions taking into account the scattering of the carriers by both piezoelectric and deformation potential acoustic phonons. We compare these results with indirect measurements of the energy relaxation time from energy loss measurements involving Joule heating of the electron gas.
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Shangina, E. L., Smirnov, K. V., Morozov, D. V., Kovalyuk, V. V., Gol’tsman, G. N., Verevkin, A. A., et al. (2010). Frequency bandwidth and conversion loss of a semiconductor heterodyne receiver with phonon cooling of two-dimensional electrons. Semicond., 44(11), 1427–1429.
Abstract: The temperature and concentration dependences of the frequency bandwidth of terahertz heterodyne AlGaAs/GaAs detectors based on hot electron phenomena with phonon cooling of two-dimensional electrons have been measured by submillimeter spectroscopy with a high time resolution. At a temperature of 4.2 K, the frequency bandwidth at a level of 3 dB (f 3 dB) is varied from 150 to 250 MHz with a change in the concentration n s according to the power law f 3dB ∝ n −0.5 s due to the dominant contribution of piezoelectric phonon scattering. The minimum conversion loss of the semiconductor heterodyne detector is obtained in structures with a high carrier mobility (μ > 3 × 105 cm2 V−1 s−1 at 4.2 K).
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Verevkin, A. A., Ptitsina, N. G., Smirnov, K. V., Voronov, B. M., Gol’tsman, G. N., Gershenson, E. M., et al. (1999). Multiple Andreev reflection in hybrid AlGaAs/GaAs structures with superconducting NbN contacts. Semicond., 33(5), 551–554.
Abstract: The conductivity of hybrid microstructures with superconducting contacts made of niobium nitride to a semiconductor with a two-dimensional electron gas in a AlGaAs/GaAs heterostructure has been investigated. Distinctive features of the behavior of the conductivity indicate the presence of multiple Andreev reflection at scattering centers in the normal region near the superconductor-semiconductor boundary.
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Verevkin, A., Zhang, J., Pearlman, A., Slysz, W., Sobolewski, R., Korneev, A., et al. (2004). Ultimate sensitivity of superconducting single-photon detectors in the visible to infrared range.
Abstract: We present our quantum efficiency (QE) and noise equivalent power (NEP) measurements of the meandertype ultrathin NbN superconducting single-photon detector in the visible to infrared radiation range. The nanostructured devices with 3.5-nm film thickness demonstrate QE up to~ 10% at 1.3–1.55 µm wavelength, and up to 20% in the entire visible range. The detectors are sensitive to infrared radiation with the wavelengths down to~ 10 µm. NEP of about 2× 10-18 W/Hz1/2 was obtained at 1.3 µm wavelength. Such high sensitivity together with GHz-range counting speed, make NbN photon counters very promising for efficient, ultrafast quantum communications and another applications. We discuss the origin of dark counts in our devices and their ultimate sensitivity in terms of the resistive fluctuations in our superconducting nanostructured devices.
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Korneev, A., Minaeva, O., Rubtsova, I., Milostnaya, I., Chulkova, G., Voronov, B., et al. (2005). Superconducting single-photon ultrathin NbN film detector. Quantum Electronics, 35(8), 698–700.
Abstract: Superconducting single-photon ultrathin NbN film detectors are studied. The development of manufacturing technology of detectors and the reduction of their operating temperature down to 2 K resulted in a considerable increase in their quantum efficiency, which reached in the visible region (at 0.56 μm) 30%—40%, i.e., achieved the limit determined by the absorption coefficient of the film. The quantum efficiency exponentially decreases with increasing wavelength, being equal to ~20% at 1.55 μm and ~0.02% at 5 μm. For the dark count rate of ~10-4s-1, the experimental equivalent noise power was 1.5×10-20 W Hz-1/2; it can be decreased in the future down to the record low value of 5×10-21 W Hz-1/2. The time resolution of the detector is 30 ps.
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Slysz, W., Wegrzecki, M., Bar, J., Grabiec, P., Górska, M., Latta, C., et al. (2005). Fiber-coupled quantum-communications receiver based on two NbN superconducting single-photon detectors. In A. Rogalski, E. L. Dereniak, & F. F. Sizov (Eds.), Proc. SPIE (Vol. 5957, 59571K (1 to 10)). SPIE.
Abstract: We present the design and performance of a novel, two-channel single-photon receiver, based on two fiber-coupled NbN superconducting single-photon detectors (SSPDs). The SSPDs are nanostructured superconducting meanders covering an area of 100 μm2 and are known for ultrafast and efficient counting of single, visible-to-infrared photons. Their operation has been explained within a phenomenological hot-electron photoresponse model. Our receiver is intended for fiber-based quantum cryptography and communication systems, operational at near-infrared (NIR) telecommunication wavelengths, λ = 1.3 μm and λ = 1.55 μm. Coupling between the NbN detector and a single-mode optical fiber was achieved using a specially designed, micromechanical photoresist ring, positioned directly over the SSPD active area. The positioning accuracy of the ring was below 1 μm. The receiver with SSPDs was placed (immersed) in a standard liquid-helium transport Dewar and kept without interruption for over two months at 4.2 K. At the same time, the optical fiber inputs and electrical outputs were kept at room temperature. Our best system reached a system quantum efficiency of up to 0.3 % in the NIR radiation range, with the detector coupling efficiency of about 30 %. The response time was measured to be about 250 ps and was limited by our read-out electronics. The measured jitter was close to 35 ps. The presented performance parameters show that our NIR single photon detectors are suitable for practical quantum cryptography and for applications in quantum-correlation experiments.
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Goltsman, G., Korneev, A., Minaeva, O., Rubtsova, I., Chulkova, G., Milostnaya, I., et al. (2005). Advanced nanostructured optical NbN single-photon detector operated at 2.0 K. In M. Razeghi, & G. J. Brown (Eds.), Proc. SPIE (Vol. 5732, pp. 520–529). Spie.
Abstract: We present our studies on quantum efficiency (QE), dark counts, and noise equivalent power (NEP) of the latest generation of nanostructured NbN superconducting single-photon detectors (SSPDs) operated at 2.0 K. Our SSPDs are based on 4 nm-thick NbN films, patterned by electron beam lithography as highly-uniform 100÷120-nm-wide meander-shaped stripes, covering the total area of 10x10 μm2 with the meander filling factor of 0.7. Advances in the fabrication process and low-temperature operation lead to QE as high as 30-40% for visible-light photons (0.56 μm wavelength)-the saturation value, limited by optical absorption of the NbN film. For 1.55 μm photons, QE was 20% and decreased exponentially with the wavelength reaching 0.02% at the 5-μm wavelength. Being operated at 2.0-K temperature the SSPDs revealed an exponential decrease of the dark count rate, what along with the high QE, resulted in the NEP as low as 5x10-21 W/Hz-1/2, the lowest value ever reported for near-infrared optical detectors. The SSPD counting rate was measured to be above 1 GHz with the pulse-to-pulse jitter below 20 ps. Our nanostructured NbN SSPDs operated at 2.0 K significantly outperform their semiconducting counterparts and find practical applications ranging from noninvasive testing of CMOS VLSI integrated circuits to ultrafast quantum communications and quantum cryptography.
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