Tarkhov M, Morozov D, Mauskopf P, Seleznev V, Korneev A, Kaurova N, et al. Single photon counting detector for THz radioastronomy. In: Proc. 17th Int. Symp. Space Terahertz Technol.; 2006. p. 119–22.
Abstract: In this paper we present the results of the research on the superconducting NbN-ultrathin-film single- photon detectors (SSPD) which are capable to detect single quanta in middle IR range. The detection mechanism is based on the hotspot formation in quasi-two-dimensional superconducting structures upon photon absorption. Spectral measurements showed that up to 5.7 gm wavelength (52 THz) the SSPD exhibits single-photon sensitivity. Reduction of operation temperature to 1.6 K allowed us to measure quantum efficiency of -4% at 60 THz. Although further decrease of the operation temperature far below 1 K does not lead to any significant increase of quantum efficiency. We expect that the improvement of the SSPD's performance at reduced operation temperature will make SSPD a practical detector with high characteristics for much lower THz frequencies as well.
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Maslennikov SN, Finkel MI, Antipov SV, Polyakov SL, Zhang W, Ozhegov R, et al. Spiral antenna coupled and directly coupled NbN HEB mixers in the frequency range from 1 to 70 THz. In: Proc. 17th Int. Symp. Space Terahertz Technol. Paris, France; 2006. p. 177–9.
Abstract: We investigate both antenna coupled and directly coupled HEB mixers at several LO frequencies within the range of 2.5 THz to 70 THz. H20 (2.5+10.7 THz), and CO2 (30 THz) gas discharge lasers are used as the local oscillators. The noise temperature of antenna coupled mixers is measured at LO frequencies of 2.5 THz, 3.8 THz, and 30 THz. The results for both antenna coupled and directly coupled mixer types are compared. The devices with in—plane dimensions of 5x5 ,um 2 are pumped by LO radiation at 10.7 THz. The directly coupled HEB demonstrates nearly flat dependence of responsivity on frequency in the range of 25+64 THz.
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Jiang L, Miao W, Zhang W, Li N, Lin ZH, Yao QJ, et al. Characterization of quasi-optical NbN phonon-cooled superconducting HEB mixers. In: Proc. 17th Int. Symp. Space Terahertz Technol.; 2006. p. 55–8.
Abstract: In this paper, we thoroughly investigate the performance of quasi-optical NbN phonon-cooled superconducting hot-electron bolometer (HEB) mixers, cryogenically cooled by a close-cycled 4-K refrigerator at 500 GI-1z and 850 GHz. The uncorrected lowest receiver noise Abstract---In temperatures measured are 800 K at 500 CHz without anti-reflection coating, and 1000 K @ 850 GHz with a 50 11M thick Mylar anti-reflection coating. The dependence of receiver noise temperature on the critical current and bath temperature of HEB mixer is also investigated here. Lifetime of quasi-optical superconducting NbN HEB mixers of different volumes, room temperature resistances, and critical temperatures are thoroughly studied. Increased room temperature resistance with time over the initial resistance changes between 1 and 1.2, and the reduced critical current with time over the initial value fluctuates slightly around 0.7 for most HEB mixers even of different volumes, room temperature resistances, and critical temperatures. The critical current degrades sharply vvhile room temperature resistance varies over 1.25.
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Gao JR, Hiajenius M, Yang ZQ, Klapwijk TM, Miao W, Shi SC, et al. Direct comparison of the sensitivity of a spiral and a twin-slot antenna coupled HEB mixer at 1.6 THz. In: Proc. 17th Int. Symp. Space Terahertz Technol.; 2006. p. 59–62.
Abstract: To make a direct comparison of the sensitivity between a spiral and a twin slot antenna coupled HEB mixer, we designed both types of mixers and fabricated them in a single processing run and on the same wafer. Both mixers have similar dimensions of NbN bridges (1.5-2 pm x0.2 pm). At 1.6 THz we obtained a nearly identical receiver noise temperature from both mixers (only 5% difference), which is in a good agreement with the simulation based on semi analytical models for both antennas. In addition, by using a bandpass filter to reduce the direct detection effect and lowering the bath temperature to 2.4 K, we measured the lowest receiver noise temperature of 700 K at 1.63 THz using the twin-slot antenna mixer.
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Gao JR, Hajenius M, Tichelaar FD, Voronov B, Grishina E, Klapwijk TM, et al. Can NbN films on 3C-SiC/Si change the IF bandwidth of hot electron bolometer mixers? In: Proc. 17th Int. Symp. Space Terahertz Technol.; 2006. p. 187–9.
Abstract: We realized ultra thin NbN films sputtered grown on a 3C-SiC/Si substrate. The film with a thickness of 3.5-4.5 nm shows a 1', of 11.8 K, which is the highest I`, observed among ultra thin NbN films on different substrates. The high-resolution transmission electron microscopy (HRTEM) studies show that the film has a monocrystalline structure, confirming the epitaxial growth on the 3C-SiC. Based on a two-temperature model and input parameters from standard NbN films on Si, simulations predict that the new film can increase the IF bandwidth of a HEB mixer by about a factor of 2 in comparison to the standard films. In addition, we find standard NbN films on Si with a T c of 9.4 K have a thickness of around 5.5 nm, being thicker than expected (3.5 nm).
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