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Antipov, A. V., Seleznev, V. A., Vakhtomin, Y. B., Morozov, P. V., Vasilev, D. D., Malevannaya, E. I., et al. (2020). Investigation of WSi and NbN superconducting single-photon detectors in mid-IR range. In IOP Conf. Ser.: Mater. Sci. Eng. (Vol. 781, 012011 (1 to 5)).
Abstract: Spectral characteristics of WSi and NbN superconducting single-photon detectors with different surface resistance and width of nanowire strips have been investigated in the wavelength range of 1.3-2.5 μm. WSi structures with narrower strips demonstrated better performance for detection of single photons in longer wavelength range. The difference in normalized photon count rate for such structures reaches one order of magnitude higher in comparison with structures based on NbN thin films at 2.5 μm.
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Baeva, E. M., Titova, N. A., Kardakova, A. I., Piatrusha, S. U., & Khrapai, V. S. (2020). Universal bottleneck for thermal relaxation in disordered metallic films. Jetp Lett., 111(2), 104–108.
Abstract: 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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Dryazgov, M., Semenov, A., Manova, N., Korneeva, Y., & Korneev, A. (2020). Modelling of normal domain evolution after single-photon absorption of a superconducting strip of micron width. In J. Phys.: Conf. Ser. (Vol. 1695, 012195 (1 to 4)).
Abstract: The present paper describes a modelling of normal domain evolution in superconducting strip of micron width using solving differential equations describing the temperature and current changes. The solving results are compared with experimental data. This comparison demonstrates the high accuracy of the model. In future, it is possible to employ this model for improvement of single photon detector based on micron-scale superconducting strips.
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Elezov, M. S., Shcherbatenko, M. L., Sych, D. V., & Goltsman, G. N. (2020). Development of control method for an optimal quantum receiver. In J. Phys.: Conf. Ser. (Vol. 1695, 012126).
Abstract: We propose a method for optimal displacement controlling of an optimal quantum receiver for registrations a binary coherent signal. An optimal receiver is able to distinguish between two phase-modulated states of a coherent signal. The optimal receiver controlling method can be used later in practice in various physical implementations of the optimal receiver.
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Elmanov, I., Sardi, F., Xia, K., Kornher, T., Kovalyuk, V., Prokhodtsov, A., et al. (2020). Development of focusing grating couplers for lithium niobate on insulator platform. In J. Phys.: Conf. Ser. (Vol. 1695, 012127).
Abstract: In this paper, we fabricate and experimentally study focusing grating couplers for lithium niobate on an insulator photonic platform. The transmittance of a waveguide equipped with in- and out-couplers with respect to the grating period is measured with and without silicon dioxide cladding applied. Our results show the influence of silicon dioxide cladding on the efficiency and the central wavelength of grating couplers and can be used to improve grating coupling efficiency. Our study is supported by numerical simulations.
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Elmanov, I., Elmanova, A., Kovalyuk, V., An, P., & Goltsman, G. (2020). Integrated contra-directional coupler for NV-centers photon filtering. In Proc. 32-nd EMSS (pp. 354–360).
Abstract: We modelled an integrated optical contra-directional coupler on silicon nitride platform. Performance of the filter was studied depending on different parameters, including the grating period and the height of teeth of the Bragg grating near 637 nm operation wavelength. The obtained results can be used for a design and fabrication of quantum photonic integrated circuits with on-chip single-photon NV-centers in nanodiamonds.
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Elmanov, I., Elmanova, A., Kovalyuk, V., An, P., & Goltsman, G. (2020). Silicon nitride photonic crystal cavity coupled with NV-centers in nanodiamonds. In Proc. 32-nd EMSS (pp. 344–348).
Abstract: The development of integrated quantum photonics requires a high efficient excitation and coupling of a single photon source with on-chip devices. In this paper, we show our results of modelling for high-Q photonic crystal cavity, optimized for zero phonon line emission of NV-centers in nanodiamonds. Modelling was performed for the silicon nitride platform and obtained a quality factor equals to 6136 at 637 nm wavelength.
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Elmanova, A., An, P., Kovalyuk, V., Golikov, A., Elmanov, I., & Goltsman, G. (2020). Study of silicon nitride O-ring resonator for gas-sensing applications. In J. Phys.: Conf. Ser. (Vol. 1695, 012124).
Abstract: In this work, we experimentally studied the influence of different gaseous surroundings on silicon nitride O-ring resonator transmission. We compared the obtained results with numerical calculations and theoretical analysis and found a good agreement between them. Our results have a great potential for gas sensing applications, where a compact footprint and high efficiency are desired simultaneously.
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Gorokhov, G., Bychanok, D., Gayduchenko, I., Rogov, Y., Zhukova, E., Zhukov, S., et al. (2020). THz spectroscopy as a versatile tool for filler distribution diagnostics in polymer nanocomposites. Polymers (Basel), 12(12), 3037 (1 to 14).
Abstract: Polymer composites containing nanocarbon fillers are under intensive investigation worldwide due to their remarkable electromagnetic properties distinguished not only by components as such, but the distribution and interaction of the fillers inside the polymer matrix. The theory herein reveals that a particular effect connected with the homogeneity of a composite manifests itself in the terahertz range. Transmission time-domain terahertz spectroscopy was applied to the investigation of nanocomposites obtained by co-extrusion of PLA polymer with additions of graphene nanoplatelets and multi-walled carbon nanotubes. The THz peak of permittivity's imaginary part predicted by the applied model was experimentally shown for GNP-containing composites both below and above the percolation threshold. The physical nature of the peak was explained by the impact on filler particles excluded from the percolation network due to the peculiarities of filler distribution. Terahertz spectroscopy as a versatile instrument of filler distribution diagnostics is discussed.
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Komrakova, S., Kovalyuk, V., An, P., Golikov, A., Rybin, M., Obraztsova, E., et al. (2020). Effective absorption coefficient of a graphene atop of silicon nitride nanophotonic circuit. In J. Phys.: Conf. Ser. (Vol. 1695, 012135).
Abstract: In this paper, we demonstrate the results of a study of the optical absorption properties of graphene integrated with silicon nitride O-ring resonator. We fabricated an array of O-ring resonators with different graphene coverage area atop. By measuring the transmission spectra of nanophotonic devices with and without graphene, we calculated the effective absorption coefficient of the graphene on a rib silicon nitride waveguide.
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Korneeva, Y. P., Manova, N. N., Florya, I. N., Mikhailov, M. Y., Dobrovolskiy, O. V., Korneev, A. A., et al. (2020). Different single-photon response of wide and narrow superconducting MoxSi1−x strips. Phys. Rev. Applied, 13(2), 024011 (1 to 7).
Abstract: The photon count rate (PCR) of superconducting single-photon detectors made of MoxSi1−x films shaped as a 2-μm-wide strip and a 115-nm-wide meander strip line is studied experimentally as a function of the dc biasing current at different values of the perpendicular magnetic field. For the wide strip, a crossover current Icross is observed, below which the PCR increases with an increasing magnetic field and above which it decreases. This behavior contrasts with the narrow MoxSi1−x meander, for which no crossover current is observed, thus suggesting different photon-detection mechanisms in the wide and narrow strips. Namely, we argue that in the wide strip the absorbed photon destroys superconductivity locally via the vortex-antivortex mechanism for the emergence of resistance, while in the narrow meander superconductivity is destroyed across the whole strip line, forming a hot belt. Accordingly, the different photon-detection mechanisms associated with vortices and the hot belt determine the qualitative difference in the dependence of the PCR on the magnetic field.
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Kuzin, A., Elmanov, I., Kovalyuk, V., An, P., & Goltsman, G. (2020). Silicon nitride focusing grating coupler for input and output light of NV-centers. In Proc. 32-nd EMSS (pp. 349–353).
Abstract: Here we presented the numerical results for the calculation of focusing grating coupler efficiency in the visible wavelength range. Using the finite element method, the optimal geometric parameters, including filling factor and grating period for a central wavelength of 637 nm, were found. Obtained results allow to input/output single-photon radiation from NV-centers, and can be used for research and development of a scalable on-chip quantum optical computing.
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Manova, N. N., Simonov, N. O., Korneeva, Y. P., & Korneev, A. A. (2020). Developing of NbN films for superconducting microstrip single-photon detector. In J. Phys.: Conf. Ser. (Vol. 1695, 012116 (1 to 5)).
Abstract: We optimized NbN films on a Si substrate with a buffer SiO2 layer to produce superconducting microstrip single-photon detectors with saturated dependence of quantum efficiency (QE) versus normalized bias current. We varied thickness of films and observed the maximum QE saturation for device based on the thinner film with the lowest ratio RS300/RS20.
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Matyushkin, Y., Danilov, S., Moskotin, M., Belosevich, V., Kaurova, N., Rybin, M., et al. (2020). Helicity-sensitive plasmonic terahertz interferometer. Nano Lett., 20(10), 7296–7303.
Abstract: Plasmonic interferometry is a rapidly growing area of research with a huge potential for applications in the terahertz frequency range. In this Letter, we explore a plasmonic interferometer based on graphene field effect transistor connected to specially designed antennas. As a key result, we observe helicity- and phase-sensitive conversion of circularly polarized radiation into dc photovoltage caused by the plasmon-interference mechanism: two plasma waves, excited at the source and drain part of the transistor, interfere inside the channel. The helicity-sensitive phase shift between these waves is achieved by using an asymmetric antenna configuration. The dc signal changes sign with inversion of the helicity. A suggested plasmonic interferometer is capable of measuring the phase difference between two arbitrary phase-shifted optical signals. The observed effect opens a wide avenue for phase-sensitive probing of plasma wave excitations in two-dimensional materials.
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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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Matyushkin, Y., Fedorov, G., Moskotin, M., Danilov, S., Ganichev, S., & Goltsman, G. (2020). Gate-mediated helicity sensitive detectors of terahertz radiation with graphene-based field effect transistors. In Graphene and 2dm Virt. Conf..
Abstract: Closing of the so-called terahertz gap results in an increased demand for optoelectronic devices operating in the frequency range from 0.1 to 10 THz. Active plasmonic in field effect devices based on high-mobility two-dimensional electron gas (2DEG) opens up opportunities for creation of on-chip spectrum [1] and polarization [2] analysers. Here we show that single layer graphene (SLG) grown using CVD method can be used for an all-electric helicity sensitive polarization broad analyser of THz radiation. Allourresults show plasmonic nature of response. Devices are made in a configuration ofa field-effect transistor (FET) with a graphene channel that has a length of 2 mkm and a width of 5.5 mkm. Response of opposite polarity to clockwise and anticlockwise polarized radiation is due to special antenna design (see Fig.1c) as follow works [2,3]. Our approaches can be extrapolated to other 2D materials and used as a tool to characterize plasmonic excitations in them. [1]Bandurin, D. A., etal.,Nature Communications, 9(1),(2018),1-8.[2]Drexler, C.,etal.,Journal of Applied Physics, 111(12),(2012),124504.[3]Gorbenko, I. V.,et al.,physica status solidi (RRL)–Rapid Research Letters, 13(3),(2019),1800464.
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Ovchinnikov, O. V., Perepelitsa, A. S., Smirnov, M. S., Latyshev, A. N., Grevtseva, I. G., Vasiliev, R. B., et al. (2020). Luminescence of colloidal Ag2S/ZnS core/shell quantum dots capped with thioglycolic acid. J. Luminescence, 220, 117008 (1 to 7).
Abstract: The features of IR luminescence of colloidal AgS QDs passivated with thioglycolic acid (AgS/TGA) under the formation of AgS/ZnS/TGA core/shell QDs are considered. A 4.5-fold increase in the quantum yield of recombination IR luminescence within the band with a peak at 960 nm (1.29 eV), full width at half maximum of 250 nm (0.34 eV), and the Stokes shift with respect to the exciton absorption of 0.6 eV was found. The increase in the IR luminescence intensity of AgS/ZnS/TGA QDs is accompanied by an increase in the average luminescence lifetime from 2.9 ns to 14.3 ns, which is explained as “healing” of surface trap states during the formation of the ZnS shell. For the first time, the enhancement of the luminescence intensity photodegradation (hereinafter referred to as fatigue) was found during the formation of the AgS/ZnS/TGA core/shell QDs. The luminescence fatigue is irreversible. We conclude that the initial stage of photolysis of the AgS core QDs under laser irradiation plays a key role. Low-atomic photolytic clusters of silver formed on the AgS core QDs act as luminescence quenching centers and do not reveal structural transformations into AgS, provided that the clusters are not in contact with TGA.
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Pentin, I., Vakhtomin, Y., Seleznev, V., & Smirnov, K. (2020). Hot electron energy relaxation time in vanadium nitride superconducting film structures under THz and IR radiation. Sci. Rep., 10(1), 16819.
Abstract: The paper presents the experimental results of studying the dynamics of electron energy relaxation in structures made of thin (d approximately 6 nm) disordered superconducting vanadium nitride (VN) films converted to a resistive state by high-frequency radiation and transport current. Under conditions of quasi-equilibrium superconductivity and temperature range close to critical (~ Tc), a direct measurement of the energy relaxation time of electrons by the beats method arising from two monochromatic sources with close frequencies radiation in sub-THz region (omega approximately 0.140 THz) and sources in the IR region (omega approximately 193 THz) was conducted. The measured time of energy relaxation of electrons in the studied VN structures upon heating of THz and IR radiation completely coincided and amounted to (2.6-2.7) ns. The studied response of VN structures to IR (omega approximately 193 THz) picosecond laser pulses also allowed us to estimate the energy relaxation time in VN structures, which was ~ 2.8 ns and is in good agreement with the result obtained by the mixing method. Also, we present the experimentally measured volt-watt responsivity (S~) within the frequency range omega approximately (0.3-6) THz VN HEB detector. The estimated values of noise equivalent power (NEP) for VN HEB and its minimum energy level (deltaE) reached NEP@1MHz approximately 6.3 x 10(-14) W/ radicalHz and deltaE approximately 8.1 x 10(-18) J, respectively.
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Polyakova, M. I., Korneev, A. A., & Semenov, A. V. (2020). Comparison single- and double- spot detection efficiencies of SSPD based to MoSi and NbN films. In J. Phys.: Conf. Ser. (Vol. 1695, 012146 (1 to 3)).
Abstract: In this work, we present results of quantum detector tomography of superconducting single photon detector (SSPD) based on MoSi film, and compare them with previously reported data on NbN. We find that for both materials hot spot interaction length coincides with the strip width, and the dependence of single and double-spot detection efficiencies on bias current are compatible with sufficiently large hot-spot size, approaching the strip width.
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Prokhodtsov, A., Kovalyuk, V., An, P., Golikov, A., Shakhovoy, R., Sharoglazova, V., et al. (2020). Silicon nitride Mach-Zehnder interferometer for on-chip quantum random number generation. In J. Phys.: Conf. Ser. (Vol. 1695, 012118).
Abstract: In this work, we experimentally studied silicon nitride Mach-Zehnder interferometer (MZI) with two directional couplers and 400 ps optical delay line for telecom wavelength 1550 nm. We achieved the extinction ratio in a range of 0.76-13.86 dB and system coupling losses of 28-44 dB, depending on the parameters of directional couplers. The developed interferometer is promising for the use in a compact random number generator for the needs of a fully integrated quantum cryptography system, where compact design, as well as high generation speed, are needed.
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Rasulova, G. K., Pentin, I. V., Vakhtomin, Y. B., Smirnov, K. V., Khabibullin, R. A., Klimov, E. A., et al. (2020). Pulsed terahertz radiation from a double-barrier resonant tunneling diode biased into self-oscillation regime. J. Appl. Phys., 128(22), 224303 (1 to 11).
Abstract: The study of the bolometer response to terahertz (THz) radiation from a double-barrier resonant tunneling diode (RTD) biased into the negative differential conductivity region of the I–V characteristic revealed that the RTD emits two pulses in a period of intrinsic self-oscillations of current. The bolometer pulse repetition rate is a multiple of the fundamental frequency of the intrinsic self-oscillations of current. The bolometer pulses are detected at two critical points with a distance between them being half or one-third of a period of the current self-oscillations. An analysis of the current self-oscillations and the bolometer response has shown that the THz photon emission is excited when the tunneling electrons are trapped in (the first pulse) and then released from (the second pulse) miniband states.
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Shcherbatenko, M. L., Elezov, M. S., Goltsman, G. N., & Sych, D. V. (2020). Sub-shot-noise-limited fiber-optic quantum receiver. Phys. Rev. A, 101(3), 032306 (1 to 5).
Abstract: We experimentally demonstrate a quantum receiver based on the Kennedy scheme for discrimination between two phase-modulated weak coherent states. The receiver is assembled entirely from standard fiber-optic elements and operates at a conventional telecom wavelength of 1.55 μm. The local oscillator and the signal are transmitted through different optical fibers, and the displaced signal is measured with a high-efficiency superconducting nanowire single-photon detector. We show the discrimination error rate is two times below that of a shot-noise-limited receiver with the same system detection efficiency.
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Shcherbatenko, M., Elezov, M., Sych, D., & Goltsman, G. N. (2020). Optimal fiber optic scheme for sub-SQL quantum receiver realization. In J. Phys.: Conf. Ser. (Vol. 1695, 012140).
Abstract: Practical implementation of high-precision quantum measurements is an important problem in modern science. One of the main parts of the quantum receiver is the optical scheme. We developed and tested several optical circuits based on different types of interferometers, namely Sagnac-based scheme, Mach-Zehnder-based scheme, and Michelson-based scheme. All these schemes are assembled with optical fibers and fiber-optic components, since the fiber-optic implementation is closest to application in practical devices. Schemes were evaluated according to two main criteria: extinction and interference stability. On the basis of the obtained data, it can be concluded that the most suitable is the scheme based on the Mach-Zehnder interferometer. In continuous mode, we were able to obtain an interference extinction about 30 dB with acceptable temporal stability.
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Shein, K. V., Zarudneva, A. A., Emel’yanova, V. O., Logunova, M. A., Chichkov, V. I., Sobolev, A. S., et al. (2020). Superconducting microstructures with high impedance. Phys. Solid State, 62(9), 1539–1542.
Abstract: The transport properties of two types of quasi-one-dimensional superconducting microstructures were investigated at ultra-low temperatures: the narrow channels close-packed in the shape of meander, and the chains of tunneling contacts “superconductor-insulator-superconductor.” Both types of the microstructures demonstrated high value of high-frequency impedance and-or the dynamic resistance. The study opens up potential for using of such structures as current stabilizing elements with zero dissipation.
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Shurakov, A., Mikhailov, D., Belikov, I., Kaurova, N., Zilberley, T., Prikhodko, A., et al. (2020). Planar Schottky diode with a Γ-shaped anode suspended bridge. In J. Phys.: Conf. Ser. (Vol. 1695, 012154).
Abstract: In this paper we report on the fabrication of a planar Schottky diode utilizing a Г-shaped anode suspended bridge. The bridge maintains transition between the top and bottom level planes of a 1.4 µm thick GaAs mesa. To implement the profile of a suspended bridge and inward tilt of a mesa wall adjacent to it, we make use of an anisotropic etching of gallium arsenide. The geometry proposed enables the fabrication of a diode with mesa of an arbitrary thickness to mitigate AC losses in the diode layered structure at terahertz frequencies of interest. For frequencies beyond 1 THz, it is also beneficial to use the geometry for the implementation of n-GaAs/n-InGaAs heterojunction Schottky diodes grown on InP substrate.
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Shurakov, A., Prikhodko, A., Mikhailov, D., Belikov, I., Kaurova, N., Voronov, B., et al. (2020). Efficiency of a microwave reflectometry for readout of a THz multipixel Schottky diode direct detector. In J. Phys.: Conf. Ser. (Vol. 1695, 012156).
Abstract: In this paper we report on the results of investigation of efficiency of a microwave reflectometry for readout of a terahertz multipixel Schottky diode direct detector. Decent capabilities of the microwave reflectometry readout were earlier justified by us for a hot electron bolometric direct detector. In case of a planar Schottky diode, we observed increase of an optical noise equivalent power by a factor of 2 compared to that measured within a conventional readout scheme. For implementation of a multipixel camera, a microwave reflectometer is to be used to readout each row of the camera, and the row switching is to be maintained by a CMOS analog multiplexer. The diodes within a row have to be equipped with filters to distribute the probing microwave signal properly. The simultaneous use of analog multiplexing and microwave reflectometry enables to reduce the camera response time by a factor of its number of columns.
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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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Simonov, N. O., Korneeva, Y. P., Korneev, A. A., & Goltsman, G. N. (2020). Enhance of the superconducting properties of the NbN/Au bilayer bridges. In J. Phys.: Conf. Ser. (Vol. 1695, 012132 (1 to 4)).
Abstract: We experimentally demonstrate strong temperature dependence of the critical current of the superconducting 600-nm-wide and 5-μm-long bridge made of NbN/Au bilayer. The result is achieved due to the proximity effect realized between the highly disordered superconducting NbN layer and low resistive normal-metal Au layer.
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Titova, N. A., Baeva, E. M., Kardakova, A. I., & Goltsman, G. N. (2020). Fabrication of NbN/SiNx:H/SiO2 membrane structures for study of heat conduction at low temperatures. In J. Phys.: Conf. Ser. (Vol. 1695, 012190).
Abstract: Here we report on the development of NbN/SiNx:H/SiO2-membrane structures for investigation of the thermal transport at low temperatures. Thin NbN films are known to be in the regime of a strong electron-phonon coupling, and one can assume that the phononic and electronic baths in the NbN are in local equilibrium. In such case, the cooling of the NbN-based devices strongly depends on acoustic matching to the substrate and substrate thermal characteristics. For the insulating membrane much thicker than the NbN film, our preliminary results demonstrate that the membrane serves as an additional channel for the thermal relaxation of the NbN sample. That implies a negligible role of thermal boundary resistance of the NbN-SiNx:H interface in comparison with the internal thermal resistance of the insulating membrane.
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Tretyakov, I., Svyatodukh, S., Perepelitsa, A., Ryabchun, S., Kaurova, N., Shurakov, A., et al. (2020). Ag2S QDs/Si heterostructure-based ultrasensitive SWIR range detector. Nanomaterials (Basel), 10(5), 1–12.
Abstract: In the 20(th) century, microelectronics was revolutionized by silicon-its semiconducting properties finally made it possible to reduce the size of electronic components to a few nanometers. The ability to control the semiconducting properties of Si on the nanometer scale promises a breakthrough in the development of Si-based technologies. In this paper, we present the results of our experimental studies of the photovoltaic effect in Ag2S QD/Si heterostructures in the short-wave infrared range. At room temperature, the Ag2S/Si heterostructures offer a noise-equivalent power of 1.1 x 10(-10) W/ radicalHz. The spectral analysis of the photoresponse of the Ag2S/Si heterostructures has made it possible to identify two main mechanisms behind it: the absorption of IR radiation by defects in the crystalline structure of the Ag2S QDs or by quantum QD-induced surface states in Si. This study has demonstrated an effective and low-cost way to create a sensitive room temperature SWIR photodetector which would be compatible with the Si complementary metal oxide semiconductor technology.
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Vasilev, D. D., Malevannaya, E. I., Moiseev, K. M., Zolotov, P. I., Antipov, A. V., Vakhtomin, Y. B., et al. (2020). Influence of deposited material energy on superconducting properties of the WSi films. In IOP Conf. Ser.: Mater. Sci. Eng. (Vol. 781, 012013 (1 to 6)).
Abstract: WSi thin films have the advantages for creating SNSPDs with a large active area or array of detectors on a single substrate due to the amorphous structure. The superconducting properties of ultrathin WSi films substantially depends on their structure and thickness as the NbN films. Scientific groups investigating WSi films mainly focused only on changes of their thickness and the ratio of the components on the substrate at room temperature. This paper presents experiments to determine the effect of the bias potential on the substrate, the temperature of the substrate, and the peak power of pulsed magnetron sputtering, which is the equivalent of ionization, a tungsten target, on the surface resistance and superconducting properties of the WSi ultrathin films. The negative effect of the substrate temperature and the positive effect of the bias potential and the ionization coefficient (peak current) allow one to choose the best WSi films formation mode for SNSPD: substrate temperature 297 K, bias potential -60 V, and peak current 3.5 A.
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Venediktov, I. O., Elezov, M. S., Prokhodtsov, A. I., Kovalyuk, V. V., An, P. P., Golikov, A. D., et al. (2020). Study of microheater’s phase modulation for on-chip Kennedy receiver. In J. Phys.: Conf. Ser. (Vol. 1695, 012117).
Abstract: In this work we describe phase modulators for several Mach-Zehnder interferometers (MZI) on silicon nitride platform for telecomm wavelength (1550 nm). We obtained current-voltage and phase-voltage curves for these modulators. MZI are needed for experimental realisation of various quantum receivers that can distinguish weak coherent states of light with extremely low error. Thermo-optical (TO) modulation is ensured by microheaters on one of the arms of MZI, which enables the change of the refractive index of the material with temperature. This approach allows to apply the necessary voltage to the golden microheaters to obtain the required phase change. For the on-chip microheaters we demonstrate the dependence of the phase shift on the voltage applied to our on-chip microheaters.
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Vodolazov, D. Y., Manova, N. N., Korneeva, Y. P., & Korneev, A. A. (2020). Timing jitter in NbN superconducting microstrip single-photon detector. Phys. Rev. Applied, 14(4), 044041 (1 to 8).
Abstract: We experimentally study timing jitter of single-photon detection by NbN superconducting strips with width w ranging from 190 nm to 3μm. We find that timing jitter of both narrow (190 nm) and micron-wide strips is about 40 ps at currents where internal detection efficiency η saturates and it is close to our instrumental jitter. We also calculate intrinsic timing jitter in wide strips using the modified time-dependent Ginzburg-Landau equation coupled with a two-temperature model. We find that with increasing width the intrinsic timing jitter increases and the effect is most considerable at currents where a rapid growth of η changes to saturation. We relate it with complicated vortex and antivortex dynamics, which depends on a photon’s absorption site across the strip and its width. The model also predicts that at current close to depairing current the intrinsic timing jitter of a wide strip could be about ℏ/kBTc (Tc is a critical temperature of superconductor), i.e., the same as for a narrow strip.
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Zhang, X., Lita, A. E., Smirnov, K., Liu, H. L., Zhu, D., Verma, V. B., et al. (2020). Strong suppression of the resistivity near the superconducting transition in narrow microbridges in external magnetic fields. Phys. Rev. B, 101(6), 060508 (1 to 6).
Abstract: We have investigated a series of superconducting bridges based on homogeneous amorphous WSi and MoSi films, with bridge widths w ranging from 2 to 1000μm and film thicknesses d∼4−6 and 100 nm. Upon decreasing the bridge widths below the respective Pearl lengths, we observe in all cases distinct changes in the characteristics of the resistive transitions to superconductivity. For each of the films, the resistivity curves R(B,T) separate at a well-defined and field-dependent temperature T∗(B) with decreasing the temperature, resulting in a dramatic suppression of the resistivity and a sharpening of the transitions with decreasing bridge width w. The associated excess conductivity in all the bridges scales as 1/w, which may suggest either the presence of a highly conducting region that is dominating the electric transport, or a change in the vortex dynamics in narrow enough bridges. We argue that this effect can only be observed in materials with sufficiently weak vortex pinning.
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Zvagelsky, R. D., Chubich, D. A., Kolymagin, D. A., Korostylev, E. V., Kovalyuk, V. V., Prokhodtsov, A. I., et al. (2020). Three-dimensional polymer wire bonds on a chip: morphology and functionality. J. Phys. D: Appl. Phys., 53(35), 355102.
Abstract: Modern microchip-scale transceivers are capable of transmitting data at rates of the order of several terabits per second. In this regard, there is an urgent need to improve the interfaces connecting the chips and extend the bandpass of the interconnections. We use an approach combining silicon nitride nanophotonic circuits with 3D polymer waveguides fabricated by direct laser writing, which can be used as photonic interconnections or photonic wire bonds (PWB). These structures are designed, simulated, fabricated, and optimized for better light transmission at the telecommunication wavelength. An important part of this work is the study of the telecom signal transmission in a 3D polymer waveguide connecting two silicon nitride facing tapers. Two cases are considered: the tapers are one opposite the other or misaligned. Initially, the PWB shape was chosen to be Gaussian and then optimized: the top was circle-shaped and with the lower part still being Gaussian. Transmission losses were measured for both types of waveguides with different shapes. The idea of an optical multi-level crossing for photonic integrated circuits is also suggested as a solution to the problem of interconnections within a single chip.
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