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Гольцман, Г. Н.; Веревкин, А. А.; Гершензон, Е. М.; Птицина, Н. Г.; Смирнов, К. В.; Чулкова, Г. М. |
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Исследования процессов неупругой релаксации и примесная спектроскопия-релаксометрия в двумерном электронном газе в полупроводниковых структурах с квантовыми ямами |
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1995 |
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В гетероструктурах GaAs/AlGaAs впервые прямым методом измерена температурная зависимость вpемени энеpгетической pелаксации двумерного электронного газа te(T) в широком диапазоне температур Т=1,5 – 50 К в квазиравновесных условиях. Для измерений использовался высокочувствительный спектрометр миллиметрового диапазона волн с высоким временным разрешением, который позволял измерять релаксационные времена до 150 пс с погрешностью не более 20%. Верхний предел температуры определялся временным разрешением спектрометра. Исследования проводились на высококачественных образцах с поверхностной концентрацией носителей ns = 4,2 1011 см-2 и подвижностью m = 7 105 см2В-1с-1 (при Т = 4,2К). В квазиравновесных условиях из температурной зависимости tе определен предел подвижности при низких температурах (T<4.2 K), связанный с рассеянием на пьезоакустическом потенциале, получено время неупругой релаксации, связанное с рассеянием на деформационном потенциале (15 K25 K), получено характерное время испускания оптического фонона (tLO>4,5пс), которое существенно превышает время сронтанного излучения оптического фонона (примерно в 30 раз), что связано с большой ролью процессов перепоглащения фононов электронами.При низких температурах проведены измерения tе в условиях сильного разогрева. Полученные значения tе и зависимость tе от температуры электронов Те совпадают с tе(Т) в квазиравновесных условиях при Т=Те. Из полученных значений tе(Те) построена зависимость мощности энергетических потерь от Те, которая хорошо согласуется с литературными данными.Начаты измерения в магнитном поле, которые показывают переспективность использованного нами метода измерений как в области слабых магнитных полей при факторе заполнения >10, так и в области сильных магнитных полей при факторе заполнения >1-2. |
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Отчет о НИР/НИОКР; РФФИ: 95-02-06409-а; |
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1831 |
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Gol'tsman, G. N.; Karasik, B. S.; Okunev, O. V.; Dzardanov, A. L.; Gershenzon, E. M.; Ekstrom, H.; Jacobsson, S.; Kollberg, E. |
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NbN hot electron superconducting mixers for 100 GHz operation |
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1995 |
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IEEE Trans. Appl. Supercond. |
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IEEE Trans. Appl. Supercond. |
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5 |
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2 |
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3065-3068 |
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NbN HEB mixers |
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NbN is a promising superconducting material for hot-electron superconducting mixers with an IF bandwidth larger than 1 GHz. In the 1OO GHz frequency range, the following parameters were obtained for 50 /spl Aring/ thick NbN films at 4.2 K: receiver noise temperature (DSB) /spl sim/1000 K; conversion loss /spl sim/10 dB; IF bandwidth /spl sim/1 GHz; and local oscillator power /spl sim/1 /spl mu/W. An increase of the critical current of the NbN film, increased working temperature, and a better mixer matching may allow a broader IF bandwidth up to 2 GHz, reduced conversion losses down to 3-5 dB and a receiver noise temperature (DSB) down to 200-300 K. |
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1051-8223 |
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About LO power required |
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Hans Ekstrom; Karasik, Boris S.; Kollberg, Erik L.; Sigfrid Yngvesson |
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Conversion gain and noise of niobium superconducting hot–electron–mixers |
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1995 |
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IEEE Trans. Appl. Supercond. |
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43 |
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4 |
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938-947 |
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Nb HEB mixers |
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254 |
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Karasik, B. S.; Elantiev, A. I. |
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Analysis of the noise performance of a hot-electron superconducting bolometer mixer |
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1995 |
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Proc. 6th Int. Symp. Space Terahertz Technol. |
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Proc. 6th Int. Symp. Space Terahertz Technol. |
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229-246 |
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HEB mixers |
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A theoretical analysis for the noise temperature of hot–electron superconducting mixer has been presented. Thecontributions of both Johnson noise and electron temperature fluctuations have been evaluated. A set of criteriaensuring low noise performance of the mixer has been stated and a simple analytic expression for the noisetemperature of the mixer device has been suggested. It has been shown that an improvement of the mixer sensitivitydoes not necessarily follow by a decrease of the bandwidth. An SSB noise temperature limit due to the intrinsic noisemechanisms has been estimated to be as low as 40–90 K for a mixer device made from Nb or NbN thin film.Furthermore, the conversion gain bandwidth can be as wide as is allowed by the intrinsic electron temperaturerelaxation time if an appropriate choice of the mixer resistance has been made. The intrinsic mixer noise bandwidthis of 3 GHz for Nb device and of 5 GHz for NbN device. An additional improvement of the theory has been madewhen a distinction between the impedance measured at high intermediate frequency (larger than the mixerbandwidth) and the mixer ohmic resistance has been taken into account.Recently obtained experimental data on Nb and NbNbolometer mixer devices are viewed in connection with thetheoretical predictions.The noise temperature limit has also been specified for the mixer device where an outdiffusion coolingmechanism rather than the electron–phonon energy relaxation determines the mixer bandwidth. A consideration ofthe noise performance of a bolometer mixer made from YBaCuO film utilizing a hot–electron effect has been done. |
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Kerr, A. R. |
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Some fundamental and practical limits on broadband matching tocapacitive devices, and the implications for SIS mixer design |
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1995 |
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IEEE Trans. Microw. Theory Techn. |
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43 |
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1 |
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2-13 |
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de Lange, G.; Kuipers, J. J.; Klapwijk, T. M.; Panhuyzen, R. A.; van de Stadt, H.; de Graauw, M. W. M. |
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Superconducting resonator circuits at frequencies above the gap frequency |
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1995 |
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J. Appl. Phys. |
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77 |
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4 |
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1795-1804 |
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Hesler, J. L.; Crowe, T. W.; Bradley, R. F.; Pan, S. K.; Chattopadhyay, G. |
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The design, construction and evaluation of a 585 GHz planar Schottky mixer |
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1995 |
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Proc. 6th Int. Symp. Space Terahertz Technol. |
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34-43 |
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Parvitte, B.; Thomas, X.; Courtois, D. |
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Wide band (2.5 GHz) infrared heterodyne spectrometer |
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1995 |
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Int. J. Infrared and Millimeter Waves |
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16 |
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9 |
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1533-1540 |
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HgCdTe detector mixer |
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0195-9271 |
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Semenov, A. D.; Nebosis, R. S.; Gousev, Yu. P.; Heusinger, M. A.; Renk, K. F. |
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Analysis of the nonequilibrium photoresponse of superconducting films to pulsed radiation by use of a two-temperature model |
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1995 |
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Phys. Rev. B |
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Phys. Rev. B |
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52 |
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581-590 |
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HEB, NbN phonon scecific heat, Cp |
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Photoresponse of a superconducting film in the resistive state to pulsed radiation has been studied in the framework of a model assuming that two different effective temperatures can be assigned to the quasiparticle and phonon nonequilibrium distributions. The coupled electron-phonon-substrate system is described by a system of time-dependent energy-balance differential equations for effective temperatures. An analytical solution of the system is given and calculated voltage transients are compared with experimental photoresponse signals taking into account the radiation pulse shape and the time resolution of the readout electronics. It is supposed that a resistive state (vortices, fluxons, network of intergrain junctions, hot spots, phase slip centers) provides an ultrafast connection between electron temperature changes and changes of the film resistance and thus plays a minor role in the temporal evolution of the response. In accordance with experimental observations a two-component response was revealed from simulations. The slower component corresponds to a bolometric mechanism while the fast component is connected with the relaxation of the electron temperature. Calculated photoresponse transients are presented for different ratios of the electron and phonon specific heat, radiation pulse durations and fluences, and frequency band passes of registration electronics. From the amplitude of the bolometric component we determine the radiation energy absorbed in a film. This enables us to reveal an intrinsic electron-phonon scattering time even if it is much shorter than the time resolution of readout electronics. We analyze experimental voltage transients for NbN, YBa2Cu3O7, and TlBa2Ca2Cu3O9 superconducting films and find the electron-phonon interaction times at the transition temperatures of 17, 2.5, and 1.8 ps, respectively. The values are in reasonable agreement with data of other experiments. |
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Krasnosvobodtsev, S. I.; Shabanova, N,P.; Ekimov, E.V.; Nozdrin, V.S.; Pechen, E,V. |
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Critical magnetic field of NbC: new data on clean superconductor films |
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1995 |
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Zh. Eks. Teor.Fiz. |
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534-537 |
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The temperature dependence of the upper critical magnetic fields of exceptionally low-defect-density films of the superconducting compound NbC has been investigated, and previously unknown parameters of this clean superconductor and its electronic characteristics have been evaluated. An electron density of states at the Fermi level equal to 1.3 states/ eV. Nb atom, a Fermi velocity equal to 2.2X lo7 cmls, a plasma frequency equal to 3.6 eV, and a coherence length to 24 nm have been obtained with an electron mean free path exceeding 40 nm. A vortex-free state existing over the entire temperature range below T, which causes a many-fold increase in the critical magnetic field of the films when the field is aligned parallel to their surface, has been discovered in very thin films of superconducting niobium carbide. |
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