Yagoubov P, Kroug M, Merkel H, Kollberg E, Hübers H-W, Schubert J, et al. NbN hot electron bolometric mixers at frequencies between 0.7 and 3.1 THz. In: Proc. 10th Int. Symp. Space Terahertz Technol.; 1999. p. 238–46.
Abstract: The performance of NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixers is investigated in the 0.7-3.1 THz frequency range. The devices are made from a 3.5-4 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The length of the bolometer microbridge is 0.1- 0.2 gm, the width is 1-2 gm. The best results of the DSB receiver noise temperature measured at 1.5 GHz intermediate frequency are: 800 K at 0.7 THz, 1100 K at 1.6 THz, 2000 K at 2.5 THz and 4200 K at 3.1 THz. The measurements were performed with a far infrared laser as the local oscillator (LO) source. The estimated LO power required is less than 500 nW at the receiver input. First results on the spiral antenna polarization measurements are reported.
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Okunev 0., Dzardranov A, Gol'tsman G, Gershenzon E. Performances of hot—electron superconducting mixer for frequencies less than the gap energy: NbN mixer for 100 GHz operation. In: Proc. 6th Int. Symp. Space Terahertz Technol.; 1995. p. 247–53.
Abstract: The possibilities to improve the parameters of the 100 GHz NbN HEB superconducting waveguide mixers have been studied. The device consists of a signal strip 1 gm wide by 2 Am long made of 40 A thick NbN film. The best operation point was found at 5 K, where the mixer bandwidth made up 1.5-2 GHz and the total loss diminished down to 8 dB. The critical current density has been increased up to " 40 6 A/cm 2 , the noise temperature of the receiver (DSB) has reduced down to 450 K and the local oscillator power has decreased down to -.4).1 mcV.
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Gershenzon EM, Gol'tsman GN, Ptitsina NG. Submillimeter spectroscopy of semiconductors. Sov Phys JETP. 1973;37(2):299–304.
Abstract: The possibility is considered of carrying out submillimeter-wave spectral investigations of semiconductors by means of a high resolution spectrometer with backward-wave tubes. Results of a study of the excitation spectra of small impurities, D-(A +) centers and free excitons in germanium are presented.
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Lindgren M, Currie M, Zeng W-S, Sobolewski R, Cherednichenko S, Voronov B, et al. Picosecond response of a superconducting hot-electron NbN photodetector. Appl Supercond. 1998;6(7-9):423–8.
Abstract: The ps optical response of ultrathin NbN photodetectors has been studied by electro-optic sampling. The detectors were fabricated by patterning ultrathin (3.5 nm thick) NbN films deposited on sapphire by reactive magnetron sputtering into either a 5×10 μm2 microbridge or 25 1 μm wide, 5 μm long strips connected in parallel. Both structures were placed at the center of a 4 mm long coplanar waveguide covered with Ti/Au. The photoresponse was studied at temperatures ranging from 2.15 K to 10 K, with the samples biased in the resistive (switched) state and illuminated with 100 fs wide laser pulses at 395 nm wavelength. At T=2.15 K, we obtained an approximately 100 ps wide transient, which corresponds to a NbN detector response time of 45 ps. The photoresponse can be attributed to the nonequilibrium electron heating effect, where the incident radiation increases the temperature of the electron subsystem, while the phonons act as the heat sink. The high-speed response of NbN devices makes them an excellent choice for an optoelectronic interface for superconducting digital circuits, as well as mixers for the terahertz regime. The multiple-strip detector showed a linear dependence on input optical power and a responsivity =3.9 V/W.
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Gershenzon EM, Gol'tsman GN, Dzardanov AL, Kuznetsov EA. Superconducting UHF-limiter based on electron heating up. Sverkhprovodimost': Fizika, Khimiya, Tekhnika. 1992;5(11):2164–70.
Abstract: The results of experimental investigation of fast-action 5HF-limiter are presented; the limiter is based on the utilization of electron hetaing phenomenon in thin superconducting films. The design of SHF-limiter, which is intended for operation at liquid helium temperatures and which has the form of a section of superconducting NbN microstrip line for 1-12 GHz rang, is described.
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