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Gol'tsman, G. N., Vachtomin, Y. B., Antipov, S. V., Finkel, M. I., Maslennikov, S. N., Smirnov, K. V., et al. (2005). NbN phonon-cooled hot-electron bolometer mixer for terahertz heterodyne receivers. In Proc. SPIE (Vol. 5727, pp. 95–106).
Abstract: We present the results of our studies of NbN phonon-cooled HEB mixers at terahertz frequencies. The mixers were fabricated from NbN film deposited on a high-resistivity Si substrate with an MgO buffer layer. The mixer element was integrated with a log-periodic spiral antenna. The noise temperature measurements were performed at 2.5 THz and at 3.8 THz local oscillator frequencies for the 3 x 0.2 μm2 active area devices. The best uncorrected receiver noise temperatures found for these frequencies are 1300 K and 3100 K, respectively. A water vapour discharge laser was used as the LO source. The largest gain bandwidth of 5.2 GHz was achieved for a mixer based on 2 nm thick NbN film deposited on MgO layer over Si substrate. The gain bandwidth of the mixer based on 3.5 nm NbN film deposited on Si with MgO is 4.2 GHz and the noise bandwidth for the same device amounts to 5 GHz. We also present the results of our research into decrease of the direct detection contribution to the measured Y-factor and a possible error of noise temperature calculation. The use of a square nickel cell mesh as an IR-filter enabled us to avoid the effect of direct detection and measure apparent value of the noise temperature which was 16% less than that obtained using conventional black polyethylene IR-filter.
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Baselmans, J. J. A., Baryshev, A., Reker, S. F., Hajenius, M., Gao, J. R., Klapwijk, T. M., et al. (2005). Direct detection effect in small volume hot electron bolometer mixers. Appl. Phys. Lett., 86(16), 163503 (1 to 3).
Abstract: We measure the direct detection effect in a small volume (0.15μm×1μm×3.5nm)(0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electronbolometermixer at 1.6THz1.6THz. We find that the small signal sensitivity of the receiver is underestimated by 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300K300K and 77K77K. Using a 200GHz200GHzbandpass filter at 4.2K4.2K the direct detection effect virtually disappears. This has important implications for the calibration procedure of these receivers in real telescope systems.
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Finkel, M. I., Maslennikov, S. N., & Gol'tsman, G. N. (2005). Terahertz heterodyne receivers based on superconductive hot-electron bolometer mixers. Radiophys. Quant. Electron., 48(10-11), 859–864.
Abstract: We consider recent results in development of hot-electron bolometer mixers. Special attention is paid to optimization of the contacts between the antenna and the active area of a superconducting film. An important result in the study of the parasitic effect of direct detection is obtained during the measurement of the noise temperatures by the hot/cold load method. The latest results of studies of the waveguide hot-electron bolometer mixers and their successful practical applications are considered. Progress in development of high-frequency (over 1.3 THz) heterodyne receivers for several important international projects is discussed and new submillimeter radio astronomy projects ESPRIT and SAFIR are described.
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Sobolewski, R., Xu, Y., Zheng, X., Williams, C., Zhang, J., Verevkin, A., et al. (2002). Spectral sensitivity of the NbN single-photon superconducting detector. IEICE Trans. Electron., E85-C(3), 797–802.
Abstract: We report our studies on the spectral sensitivity of superconducting NbN thin-film single-photon detectors (SPD's) capable of GHz counting rates of visible and near-infrared photons. In particular, it has been shown that a NbN SPD is sensitive to 1.55-µm wavelength radiation and can be used for quantum communication. Our SPD's exhibit experimentally measured intrinsic quantum efficiencies from 20% at 800 nm up to 1% at 1.55-µm wavelength. The devices demonstrate picosecond response time (<100 ps, limited by our readout system) and negligibly low dark counts. Spectral dependencies of photon counting of continuous-wave, 0.4-µm to 3.5-µm radiation, and 0.63-µm, 1.33-µm, and 1.55-µm laser-pulsed radiations are presented for the single-stripe-type and meander-type 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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