Semenov, A. D., & Gol'tsman, G. N. (1999). Non-thermal response of a diffusion-cooled hot-electron bolometer. IEEE Trans. Appl. Supercond., 9(2), 4491–4494.
Abstract: We present an analysis of a diffusion-cooled hot-electron bolometer in the limiting case of a weak thermalization of non-equilibrium quasiparticles. We propose a new model relying on the non-thermal suppression of the superconducting energy gap by excess quasiparticles. Using material parameters typical for Al, we evaluate performance of the bolometer in the heterodyne regime at terahertz frequencies. Estimates show that the mixer may have quantum limited noise temperature and a few tens of GHz bandwidth, while the required local oscillator power is in the /spl mu/W range due to in-effective suppression of the energy gap by quasiparticles with high energies.
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Gerecht, E., Musante, C. F., Jian, H., Yngvesson, K. S., Dickinson, J., Waldman, J., et al. (1999). New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz. IEEE Trans. Appl. Supercond., 9(2), 4217–4220.
Abstract: NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Schubert, J., Hubers, H. - W., et al. (1999). Heterodyne measurements of a NbN superconducting hot electron mixer at terahertz frequencies. IEEE Trans. Appl. Supercond., 9(2), 3757–3760.
Abstract: The performance of a NbN based phonon-cooled Hot Electron Bolometric (HEB) quasioptical mixer is investigated in the 0.65-3.12 THz frequency range. The device is made from a 3 nm thick NbN film on high resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are 0.2/spl times/2 /spl mu/m. The best results of the DSB noise temperature at 1.5 GHz IF frequency obtained with one device are: 1300 K at 650 GHz, 4700 K at 2.5 THz and 10000 K at 3.12 THz. The measurements were performed at 4.5 K ambient temperature. The amount of local oscillator (LO) power absorbed in the bolometer is about 100 nW. The mixer is linear to within 1 dB compression up to the signal level 10 dB below that of the LO. The intrinsic single sideband conversion gain measured at 650 GHz is -9 dB, the total conversion gain is -14 dB.
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Gol'tsman, G. N. (1999). Hot electron bolometric mixers: new terahertz technology. Infrared Physics & Technology, 40(3), 199–206.
Abstract: This paper presents an overview of recent results for NbN phonon-cooled hot electron bolometric (HEB) mixers. The noise temperature of the receivers based on both quasioptical and waveguide versions of HEB mixers has crossed the level of 1 K GHz−1 at 430 GHz (410 K), 600–650 GHz (480 K), 750 GHz (600 K), 810 GHz (780 K) and is close to that level at 1.1 THz (1250 K) and 2.5 THz (4500 K). The gain bandwidth measured for quasioptical HEB mixer at 620 GHz reached 4 GHz and the noise temperature bandwidth was almost 8 GHz. Local oscillator power requirements are about 1 μW for mixers made by photolithography and about 100 nW for mixers made by e-beam lithography. A waveguide version of 800 GHz receiver was installed at the Submillimeter Telescope Observatory on Mt. Graham, AZ, to conduct astronomical observations of known submillimeter lines (CO, J=7→6, CI, J=2→1). It was proved that the receiver works as a practical instrument.
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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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Sergeev, A., Karasik, B. S., Ptitsina, N. G., Chulkova, G. M., Il'in, K. S., & Gershenzon, E. M. (1999). Electron–phonon interaction in disordered conductors. Phys. Rev. B Condens. Matter, 263-264, 190–192.
Abstract: The electron–phonon interaction is strongly modified in conductors with a small value of the electron mean free path (impure metals, thin films). As a result, the temperature dependencies of both the inelastic electron scattering rate and resistivity differ significantly from those for pure bulk materials. Recent complex measurements have shown that modified dependencies are well described at K by the electron interaction with transverse phonons. At helium temperatures, available data are conflicting, and cannot be described by an universal model.
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Il’in, K. S., Milostnaya, I. I., Verevkin, A. A., Gol’tsman, G. N., Gershenzon, E. M., & Sobolewski, R. (1998). Ultimate quantum efficiency of a superconducting hot-electron photodetector. Appl. Phys. Lett., 73(26), 3938–3940.
Abstract: The quantum efficiency and current and voltage responsivities of fast hot-electron photodetectors, fabricated from superconducting NbN thin films and biased in the resistive state, have been shown to reach values of 340, 220 A/W, and 4×104 V/W,
respectively, for infrared radiation with a wavelength of 0.79 μm. The characteristics of the photodetectors are presented within the general model, based on relaxation processes in the nonequilibrium electron heating of a superconducting thin film. The observed, very high efficiency and sensitivity of the superconductor absorbing the photon are explained by the high multiplication rate of quasiparticles during the avalanche breaking of Cooper pairs.
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Yagoubov, P., Kroug, M., Merkel, H., Kollberg, E., Gol'tsman, G., Svechnikov, S., et al. (1998). Noise temperature and local oscillator power requirement of NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies. Appl. Phys. Lett., 73(19), 2814–2816.
Abstract: In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband <cd><2018>DSB<cd><2019> noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2Ï«2 um. The amount of local oscillator power absorbed in the bolometer is less than 100 nW.
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Lindgren, M., Currie, M., Zeng, W. - S., Sobolewski, R., Cherednichenko, S., Voronov, B., et al. (1998). Picosecond response of a superconducting hot-electron NbN photodetector. Appl. Supercond., 6(7-9), 423–428.
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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Il’in, K. S., Ptitsina, N. G., Sergeev, A. V., Gol’tsman, G. N., Gershenzon, E. M., Karasik, B. S., et al. (1998). Interrelation of resistivity and inelastic electron-phonon scattering rate in impure NbC films. Phys. Rev. B, 57(24), 15623–15628.
Abstract: A complex study of the electron-phonon interaction in thin NbC films with electron mean free path l=2–13nm gives strong evidence that electron scattering is significantly modified due to the interference between electron-phonon and elastic electron scattering from impurities. The interference T2 term, which is proportional to the residual resistivity, dominates over the Bloch-Grüneisen contribution to resistivity at low temperatures up to 60 K. The electron energy relaxation rate is directly measured via the relaxation of hot electrons heated by modulated electromagnetic radiation. In the temperature range 1.5–10 K the relaxation rate shows a weak dependence on the electron mean free path and strong temperature dependence ∼Tn, with the exponent n=2.5–3. This behavior is explained well by the theory of the electron-phonon-impurity interference taking into account the electron coupling with transverse phonons determined from the resistivity data.
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