Shurakov, A., Mikhalev, P., Mikhailov, D., Mityashkin, V., Tretyakov, I., Kardakova, A., et al. (2018). Ti/Au/n-GaAs planar Schottky diode with a moderately Si-doped matching sublayer. Microelectronic Engineering, 195, 26–31.
Abstract: In this paper, we report on the results of the study of the Ti/Au/n-GaAs planar Schottky diodes (PSD) intended for the wideband detection of terahertz radiation. The two types of the PSD devices were compared having either the dual n/n+ silicon dopant profile or the triple one with a moderately doped matching sublayer inserted. All the diodes demonstrated no noticeable temperature dependence of ideality factors and barrier heights, whose values covered the ranges of 1.15–1.50 and 0.75–0.85 eV, respectively. We observed the lowering of the flat band barrier height of ∼80 meV after introducing the matching sublayer into the GaAs sandwich. For both the devices types, the series resistance value as low as 20 Ω was obtained. To extract the total parasitic capacitance, we performed the Y-parameters analysis within the electromagnetic modeling of the PSD's behavior via the finite-element method. The capacitance values of 12–12.2 fF were obtained and further verified by measuring the diodes' response voltages in the frequency range of 400–480 GHz. We also calculated the AC current density distribution within the layered structures similar to those being experimentally studied. It was demonstrated that insertion of the moderately Si-doped matching sublayer might be beneficial for implementation of a PSD intended for the operation within the ‘super-THz’ frequency range.
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Shurakov, A., Seliverstov, S., Kaurova, N., Finkel, M., Voronov, B., & Goltsman, G. (2012). Input bandwidth of hot electron bolometer with spiral antenna. IEEE Trans. THz Sci. Technol., 2(4), 400–405.
Abstract: We report the results of our study of the input bandwidth of hot electron bolometers (HEB) embedded into the planar log-spiral antenna. The sensitive element is made of the ultrathin superconducting NbN film patterned as a bridge at the feed of the antenna. The contacts between the antenna and a sensitive element are made from in situ deposited gold (i.e., deposited over NbN film without breaking vacuum), which gives high quality contacts and makes the response of the HEB at higher frequencies less affected by the RF loss. An accurate experimental spectroscopic procedure is demonstrated that leads to the confirmation of the wide ( 8 THz) bandwidth in this antenna coupled device.
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Sidorova, M., Semenov, A. D., Hübers, H. - W., Ilin, K., Siegel, M., Charaev, I., et al. (2020). Electron energy relaxation in disordered superconducting NbN films. Phys. Rev. B, 102(5), 054501 (1 to 15).
Abstract: We report on the inelastic-scattering rate of electrons on phonons and relaxation of electron energy studied by means of magnetoconductance, and photoresponse, respectively, in a series of strongly disordered superconducting NbN films. The studied films with thicknesses in the range from 3 to 33 nm are characterized by different Ioffe-Regel parameters but an almost constant product qTl (qT is the wave vector of thermal phonons and l is the elastic mean free path of electrons). In the temperature range 14–30 K, the electron-phonon scattering rates obey temperature dependencies close to the power law 1/τe−ph∼Tn with the exponents n≈3.2–3.8. We found that in this temperature range τe−ph and n of studied films vary weakly with the thickness and square resistance. At 10 K electron-phonon scattering times are in the range 11.9–17.5 ps. The data extracted from magnetoconductance measurements were used to describe the experimental photoresponse with the two-temperature model. For thick films, the photoresponse is reasonably well described without fitting parameters, however, for thinner films, the fit requires a smaller heat capacity of phonons. We attribute this finding to the reduced density of phonon states in thin films at low temperatures. We also show that the estimated Debye temperature in the studied NbN films is noticeably smaller than in bulk material.
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Matyushkin, Y., Kaurova, N., Voronov, B., Goltsman, G., & Fedorov, G. (2020). On chip carbon nanotube tunneling spectroscopy. Fullerenes, Nanotubes and Carbon Nanostructures, 28(1), 50–53.
Abstract: We report an experimental study of the band structure of individual carbon nanotubes (SCNTs) based on investigation of the tunneling density of states, i.e. tunneling spectroscopy. A common approach to this task is to use a scanning tunneling microscope (STM). However, this approach has a number of drawbacks, to overcome which, we propose another method – tunneling spectroscopy of SCNTs on a chip using a tunneling contact. This method is simpler, cheaper and technologically advanced than the STM. Fabrication of a tunnel contact can be easily integrated into any technological route, therefore, a tunnel contact can be used, for example, as an additional tool in characterizing any devices based on individual CNTs. In this paper we demonstrate a simple technological procedure that results in fabrication of good-quality tunneling contacts to carbon nanotubes.
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Antipov, S., Trifonov, A., Krause, S., Meledin, D., Kaurova, N., Rudzinski, M., et al. (2019). Improved bandwidth of a 2 THz hot-electron bolometer heterodyne mixer fabricated on sapphire with a GaN buffer layer. Supercond. Sci. Technol., 32(7), 075003.
Abstract: We report on the signal-to-noise and gain bandwidth of a niobium nitride (NbN) hot-electron bolometer (HEB) mixer at 2 THz fabricated on a sapphire substrate with a GaN buffer layer. Two mixers with different DC properties and geometrical dimensions were studied and they demonstrated very close bandwidth performance. The signal-to-noise bandwidth is increased to 8 GHz in comparison to the previous results, obtained without a buffer-layer. The data were taken in a quasi-optical system with the use of the signal-to-noise method, which is close to the signal levels used in actual astrophysical observations. We find an increase of the gain bandwidth to 5 GHz. The results indicate that prior results obtained on a substrate of crystalline GaN can also be obtained on a conventional sapphire substrate with a few micron MOCVD-deposited GaN buffer-layer.
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Tretyakov, I. V., Anfertyev, V. A., Revin, L. S., Kaurova, N. S., Voronov, B. M., Vaks, V. L., et al. (2018). Sensitivity and resolution of a heterodyne receiver based on the NbN HEB mixer with a quantum-cascade laser as a local oscillator. Radiophys. Quant. Electron., 60(12), 988–992.
Abstract: We present the results of experimental studies of the basic characteristics and operation features of a terahertz heterodyne detector based on the superconducting NbN HEB mixer and a quantum cascade laser as a local oscillator operating at a frequency of 2.02 THz. The measured noise temperature of such a mixer amounted to 1500 K. The spectral resolution of the detector is determined by the width of the local-oscillator spectral line whose measured value does not exceed 1 MHz. The quantum-cascade laser could be linearly tuned with respect to frequency with the coefficient 7.2 MHz/mA within the limits of the current oscillation bandwidth.
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Fedorov, G., Gayduchenko, I., Titova, N., Gazaliev, A., Moskotin, M., Kaurova, N., et al. (2018). Carbon nanotube based schottky diodes as uncooled terahertz radiation detectors. Phys. Status Solidi B, 255(1), 1700227 (1 to 6).
Abstract: Despite the intensive development of the terahertz technologies in the last decade, there is still a shortage of efficient room‐temperature radiation detectors. Carbon nanotubes (CNTs) are considered as a very promising material possessing many of the features peculiar for graphene (suppression of backscattering, high mobility, etc.) combined with a bandgap in the carrier spectrum. In this paper, we investigate the possibility to incorporate individual CNTs into devices that are similar to Schottky diodes. The latter is currently used to detect radiation with a frequency up to 50 GHz. We report results obtained with semiconducting (bandgap of about 0.5 eV) and quasi‐metallic (bandgap of few meV) single‐walled carbon nanotubes (SWNTs). Semiconducting CNTs show better performance up to 300 GHz with responsivity up to 100 V W−1, while quasi‐metallic CNTs are shown to operate up to 2.5 THz.
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Trifonov, A., Tong, C. - Y. E., Grimes, P., Lobanov, Y., Kaurova, N., Blundell, R., et al. (2017). Development of a silicon membrane-based multipixel hot electron bolometer receiver. IEEE Trans. Appl. Supercond., 27(4), 1–5.
Abstract: We report on the development of a multipixel hot electron bolometer (HEB) receiver fabricated using silicon membrane technology. The receiver comprises a 2 × 2 array of four HEB mixers, fabricated on a single chip. The HEB mixer chip is based on a superconducting NbN thin-film deposited on top of the silicon-on-insulator (SOI) substrate. The thicknesses of the device layer and handling layer of the SOI substrate are 20 and 300 μm, respectively. The thickness of the device layer is chosen such that it corresponds to a quarter-wave in silicon at 1.35 THz. The HEB mixer is integrated with a bow-tie antenna structure, in turn designed for coupling to a circular waveguide, fed by a monolithic drilled smooth-walled horn array.
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Korneeva, Y., Florya, I., Vdovichev, S., Moshkova, M., Simonov, N., Kaurova, N., et al. (2017). Comparison of hot spot formation in nbn and mon thin superconducting films after photon absorption. IEEE Trans. Appl. Supercond., 27(4), 1–4.
Abstract: In superconducting single-photon detectors (SSPD), the efficiency of local suppression of superconductivity and hotspot formation is controlled by diffusivity and electron-phonon interaction time. Here, we selected a material, 3.6-nm-thick MoNx film, which features diffusivity close to those of NbN traditionally used for SSPD fabrication, but with electron-phonon interaction time an order of magnitude larger. In MoN ∞ detectors, we study the dependence of detection efficiency on bias current, photon energy, and strip width, and compare it with NbN SSPD. We observe nonlinear current-energy dependence in MoNx SSPD and more pronounced plateaus in dependences of detection efficiency on bias current, which we attribute to longer electron-phonon interaction time.
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Trifonov, A., Tong, C. - Y. E., Lobanov, Y., Kaurova, N., Blundell, R., & Goltsman, G. (2017). Photon absorption near the gap frequency in a hot electron bolometer. IEEE Trans. Appl. Supercond., 27(4), 1–4.
Abstract: The superconducting energy gap is a fundamental characteristic of a superconducting film, which, together with the applied pump power and the biasing setup, defines the instantaneous resistive state of the Hot Electron Bolometer (HEB) mixer at any given bias point on the I-V curve. In this paper we report on a series of experiments, in which we subjected the HEB to radiation over a wide frequency range along with parallel microwave injection. We have observed three distinct regimes of operation of the HEB, depending on whether the radiation is above the gap frequency, far below it or close to it. These regimes are driven by the different patterns of photon absorption. The experiments have allowed us to derive the approximate gap frequency of the device under test as about 585 GHz. Microwave injection was used to probe the HEB impedance. Spontaneous switching between the superconducting (low resistive) state and a quasi-normal (high resistive) state was observed. The switching pattern depends on the particular regime of HEB operation and can assume a random pattern at pump frequencies below the gap to a regular relaxation oscillation running at a few MHz when pumped above the gap.
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