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Shurakov, A.; Mikhalev, P.; Mikhailov, D.; Mityashkin, V.; Tretyakov, I.; Kardakova, A.; Belikov, I.; Kaurova, N.; Voronov, B.; Vasil’evskii, I.; Gol’tsman, G. |
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Ti/Au/n-GaAs planar Schottky diode with a moderately Si-doped matching sublayer |
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2018 |
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Microelectronic Engineering |
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Microelectronic Engineering |
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195 |
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26-31 |
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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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0167-9317 |
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1155 |
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Fedorov, G.; Kardakova, A.; Gayduchenko, I.; Voronov, B. M.; Finkel, M.; Klapwijk, T. M.; Goltsman, G. |
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Photothermoelectric response in asymmetric carbon nanotube devices exposed to sub-THz radiation |
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2014 |
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Proc. 25th Int. Symp. Space Terahertz Technol. |
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Proc. 25th Int. Symp. Space Terahertz Technol. |
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71 |
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carbon nanotubes, CNT |
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This work reports on the voltage response of asymmetric carbon nanotube devices to sub-THz radiation at the frequency of 140 GHz. The devices contain CNT’s, which are over their length partially suspended and partially Van der Waals bonded to a SiO 2 substrate, causing a difference in thermal contact. Different heat sinking of CNTs by source and drain gives rise to temperature gradient and consequent thermoelectric power (TEP) as such a device is exposed to the sub-THz radiation. Sign of the DC signal, its power and gate voltage dependence observed at room temperature are consistent with this scenario. At liquid helium temperature the observed response is more complex. DC voltage signal of an opposite sign is observed in a narrow range of gate voltages at low temperatures and under low radiation power. We argue that this may indicate a true photovoltaic response from small gap (less than 10meV) CNT’s, an effect never reported before. While it is not clear if the observed effects can be used to develop efficient THz detectors we note that the responsivity of our devices exceeds that of CNT based devices in microwave or THz range reported before at room temperature. Besides at 4.2 K notable increase of the sample conductance (at least four-fold) is observed. Our recent results with asymmetric carbon nanotube devices response to THz radiation (2.5 THz) will also be presented. |
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1361 |
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Titova, N; Kardakova, A.; Tovpeko, N; Ryabchun, S.; Mandal, S.; Morozov, D.; Klemencic, G. M.; Giblin, S.R.; Williams, O. A.; Goltsman, G. N. |
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Superconducting diamond films as perspective material for direct THz detectors |
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2017 |
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Proc. 28th Int. Symp. Space Terahertz Technol. |
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Proc. 28th Int. Symp. Space Terahertz Technol. |
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82 |
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KID, HEB, superconducting diamond films, boron-doped diamond films, Al, TiN, Si substrates, NEP |
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Superconducting films with a high resistivity in the normal state have established themselves as the best materials for direct THz radiation sensors, such as kinetic inductance detectors (KIDs) [1] and hot electron bolometers (nano-HEBs) [2]. The primary characteristics of the future instrument such as the sensitivity and the response time are determined by the material parameters such as the electron-phonon (e-ph) interaction time, the electron density and the resistivity of the material. For direct detectors, such as KIDs and nano-HEBs, to provide a high sensitivity and low noise one prefer materials with long e-ph relaxation times and low values of the electron density. As a potential material for THz radiation detection we have studied superconducting diamond films. A significant interest to diamond for the development of electronic devices is due to the evolution of its properties with the boron dopant concentration. At a high boron doping concentration, n B ~5·10 20 cm -3 , diamond has been reported to become a superconducting with T c depending on the doping level. Our previous study of energy relaxation in single-crystalline boron-doped diamond films epitaxially grown on a diamond shows a remarkably slow energy-relaxation at low temperatures. The electron-phonon cooling time varies from 400 ns to 700 ns over the temperature range 2.2 K to 1.7 K [3]. In superconducting materials such as Al and TiN, traditionally used in KIDs, the e-ph cooling times at 1.7 K correspond to ~20 ns [4] and ~100 ns [5], correspondingly. Such a noticeable slow e-ph relaxation in boron-doped diamond, in combination with a low value of carrier density (~10 21 cm -3 ) in comparison with typical metals (~10 23 cm -3 ) and a high normal state resistivity (~1500 μΩ·cm) confirms a potential of superconducting diamond for superconducting bolometers and resonator detectors. However, the price and the small substrate growth are of single crystal diamond limit practical applications of homoepitaxial diamond films. As an alternative way with more convenient technology, one can employ heteroepitaxial diamond films grown on large-size Si substrates. Here we report about measurements of e-ph cooling times in superconducting diamond grown on silicon substrate and discuss our expectations about the applicability of boron-doped diamond films to superconducting detectors. Our estimation of limit value of noise-equivalent power (NEP) and the energy resolution of bolometer made from superconducting diamond is order 10 -17 W/Hz 1/2 at 2 K and the energy resolution is of 0.1 eV that corresponds to counting single-photon up to 15 um. The estimation was obtained by using the film thickness of 70 nm and ρ ~ 1500 μΩ·cm, and the planar dimensions that are chosen to couple bolometer with 75 Ω log-spiral antenna. Although the value of NEP is far yet from what might like to have for certain astronomical applications, we believe that it can be improved by a suitable fabrication process. Also the direct detectors, based on superconducting diamond, will offer low noise performance at about 2 K, a temperature provided by inexpensive close-cycle refrigerators, which provides another practical advantage of development and application of these devices. [1] P.K. Day, et. al, Nature, 425, 817, 2003. [2] J. Wei, et al, Nature Nanotech., 3, 496, 2008. [3] A. Kardakova, et al, Phys. Rev. B, 93, 064506, 2016. [4] P. Santhanam and D. Prober, Phys. Rev. B, 29, 3733, 1984 [5] A. Kardakova, et al, Appl. Phys. Lett, vol. 103, p. 252602, 2013. |
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1173 |
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Baeva, E. M.; Titova, N. A.; Kardakova, A. I.; Piatrusha, S. U.; Khrapai, V. S. |
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Title |
Universal bottleneck for thermal relaxation in disordered metallic films |
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Journal Article |
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Year |
2020 |
Publication |
JETP Lett. |
Abbreviated Journal |
Jetp Lett. |
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111 |
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2 |
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104-108 |
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NbN disordered metallic films, thermal relaxation |
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We study the heat relaxation in current biased metallic films in the regime of strong electron–phonon coupling. A thermal gradient in the direction normal to the film is predicted, with a spatial temperature profile determined by the temperature-dependent heat conduction. In the case of strong phonon scattering, the heat conduction occurs predominantly via the electronic system and the profile is parabolic. This regime leads to the linear dependence of the noise temperature as a function of bias voltage, in spite of the fact that all the dimensions of the film are large compared to the electron–phonon relaxation length. This is in stark contrast to the conventional scenario of relaxation limited by the electron–phonon scattering rate. A preliminary experimental study of a 200-nm-thick NbN film indicates the relevance of our model for materials used in superconducting nanowire single-photon detectors. |
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0021-3640 |
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1164 |
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Elezov, M. S.; Semenov, A. V.; An, P. P.; Tarkhov, M. A.; Goltsman, G. N.; Kardakova, A. I.; Kazakov, A. Y. |
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Investigating the detection regimes of a superconducting single-photon detector |
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2013 |
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J. Opt. Technol. |
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J. Opt. Technol. |
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80 |
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7 |
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435 |
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SSPD, quantum efficiency |
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The detection regimes of a superconducting single-photon detector have been investigated. A technique is proposed for determining the regions in which “pure regimes” predominate. Based on experimental data, the dependences of the internal quantum efficiency on the bias current are determined in the one-, two-, and three-photon detection regimes. |
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1070-9762 |
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1172 |
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