Okunev, 0., Dzardranov, A., Gol'tsman, G., & Gershenzon, E. (1995). Performances of hot—electron superconducting mixer for frequencies less than the gap energy: NbN mixer for 100 GHz operation. In Proc. 6th Int. Symp. Space Terahertz Technol. (pp. 247–253).
Abstract: The possibilities to improve the parameters of the 100 GHz NbN HEB superconducting waveguide mixers have been studied. The device consists of a signal strip 1 gm wide by 2 Am long made of 40 A thick NbN film. The best operation point was found at 5 K, where the mixer bandwidth made up 1.5-2 GHz and the total loss diminished down to 8 dB. The critical current density has been increased up to " 40 6 A/cm 2 , the noise temperature of the receiver (DSB) has reduced down to 450 K and the local oscillator power has decreased down to -.4).1 mcV.
|
Гольцман, Г. Н., Веревкин, А. А., Гершензон, Е. М., Птицина, Н. Г., Смирнов, К. В., & Чулкова, Г. М. (1995). Исследования процессов неупругой релаксации и примесная спектроскопия-релаксометрия в двумерном электронном газе в полупроводниковых структурах с квантовыми ямами.
Abstract: 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.
|
Karasik, B. S., Zorin, M. A., Milostnaya, I. I., Elantev, A. I., Gol’tsman, G. N., & Gershenzon, E. M. (1994). Evidence of subnanosecond transition stage in S-N current switching of YBaCuO films. In R. A. Buhrman, J. T. Clarke, K. Daly, R. H. Koch, J. A. Luine, & R. W. Simon (Eds.), Proc. SPIE (Vol. 2160, pp. 74–82). SPIE.
Abstract: We report on a study of S-N and N-S current switching in high quality YBaCuO films deposited onto ZrO2 and NdGaO3 substrates. The films 60-120 nm thick prepared by laser ablation were structured into single strips and were provided with gold contacts. We monitored the time dependence of the resistance upon application of the voltage step on the film. Experiment performed within certain ranges of voltage amplitudes and temperatures showed the occurrence of the fast stage both in S-N (shorter than 300 ps) and N-S transition. We discuss the mechanism of switching taking into account the hot electron phenomena in YBaCuO. The contributions of various thermal processes in the subsequent stage of the resistance dynamic are also discussed. The basic limiting characteristics (average dissipated power, minimum work done for switching, maximum repetition rate) of a picosecond switch which is proposed to be developed are estimated.
|
Dzardanov, A., Ekstrom, H., Gershenzon, E., Gol'tsman, G., Jacobsson, S., Karasik, B., et al. (1994). Hot-electron superconducting mixers for 20-500 GHz operation. In Proc. Int. Conf. on Millimeter and Submillimeter Waves and Appl. (Vol. 2250, pp. 276–278).
Abstract: Bolometdcmucers based on Nb and NbN superconducting thin films in the resistive state have been prepared for 20, 100 GHz and 350-500 GHz operation. The mixing mechanism is presumably of electron heating origin. Our measurements indicate that a conversion loss of about 6-8 dB can rather easily be achieved, and that the noise is reasonably low. The requirements on the operation mode and on the film parameters in order to obtain small conversion losses or even gain are discussed. For NbN films the availability of nearly 1 GHz IF bandwidth is experimentally demonstrated. NbN hot-electron mucers combined with slot-line tapered antenna on Si membrane or with double-dipole antenna on SiO^ substrate have been fabricated. The devices we study are considered to be very promising for use in heterodyne receivers from microwaves to terahertz frequencies.
|
Ekström, H., Karasik, B., Kollberg, E., & Yngvesson, K. S. (1994). Investigation of a superconducting hot electron mixer. In Proc. 5th Int. Symp. Space Terahertz Technol. (pp. 169–188).
Abstract: Mixing at 20 GHz in niobium superconducting thin film strips in the resistive state is studied. Experiments give evidence that electron-heating is the main cause of the non linear phenomena. The requirements on the mode of operation and on the film parameters for small conversion loss and the possibility of conversion gain are discussed. Measurements indicate a minimum intrinsic conversion loss around 1 dB with a sharp drop for the lowest voltage bias-points, and a DSB mixer noise temperature between 100 and 450 K at 20 GHz. The device output noise temperature at the mixer operating point can be as low as 30-50 K. A simple theory is presented, which is based on the assumption that the small signal resistance is linearly dependent on power. This type of mixer is considered very promising for use in low-noise heterodyne receivers at THz frequencies.
|
0kunev, 0., Dzardanov, A., Ekstrom, H., Jacobsson, S., Kollberg, E., Gol'tsman, G., et al. (1994). NbN hot electron waveguide mixer for 100 GHz operation. In Proc. 5th Int. Symp. Space Terahertz Technol. (pp. 214–224).
Abstract: NbN is a promising superconducting material used to develope hot- electron superconducting mixers with an IF bandwidth over 1 GHz. In the 100 GHz frequency range, the following parameters were obtained for NbN films 50 A thick: the noise temperature of the receiver (DSB) 1000 K; the conversion losses 10 d13, the IF bandwidth 1 GHz; the local oscillator power 1 /LW. An increase of NbN film thickness up to 80-100 A and increase of working temperature up to 7-8 K, and a better mixer matching may allow to broader the IF band up to 3 Gllz, to reduce the conversion losses down to 3-5 dB and the noise tempera- ture down to 200-300 K.
|
|
Elantev, A. I., & Karasik, B. S. (1994). Noise temperature of a superconducting hot-electron mixer. In Proc. 5th Int. Symp. Space Terahertz Technol. (225).
|
Gol’tsman, G. N., Kouminov, P. B., Goghidze, I. G., Karasik, B. S., & Gershenzon, E. M. (1994). Nonbolometric and fast bolometric responses of YBaCuO thin films in superconducting, resistive, and normal states. In M. Nahum, & J. - C. Villegier (Eds.), Proc. SPIE (Vol. 2159, pp. 81–86). SPIE.
Abstract: The transient voltage response in both epitaxial and granular YBaCuO thin films to 20 ps pulses of YAG:Nd laser radiation with 0.63 micrometers and 1.54 micrometers was studied. In normal and resistive states both types of films demonstrate two components: nonequilibrium picosecond component and following bolometric nanosecond. The normalized amplitudes are almost the same for all films. In superconducting state we observed a kinetic inductive response and two-component shape after integration. The normalized amplitude of the response in granular films is up to several orders of magnitude larger than in epitaxial films. We interpret the nonequilibrium response in terms of a suppression of order parameter by the excess of quasiparticles followed by the change of resistance in normal and resistive states or kinetic inductance in superconducting state. The sharp rise of inductive response in granular films is explained both by a diminishing of the crossection for current percolation through the disordered network os Josephson weak links and by a decrease of condensate density in neighboring regions.
|
|
Gershenzon, E. M., Gol'tsman, G. N., Zorin, M. A., Karasik, B. S., & Trifonov, V. A. (1994). Nonequilibrium and bolometric response of YBaCuO films in a resistive state to infrared low intensity radiation. In Council on Low-temp. Phys. (pp. 82–83).
|
Karasik, B. S., Lindgren, M., Zorin, M. A., Danerud, M., Winkler, D., Trifonov, V. V., et al. (1994). Picosecond detection and broadband mixing of near-infrared radiation by YBaCuO films. In M. Nahum, & J. - C. Villegier (Eds.), Proc. SPIE (Vol. 2159, pp. 68–76). Spie.
Abstract: Nonequilibrium picosecond and bolometric responses of YBCO films 500 angstroms thick patterned into 20 X 20 micrometers 2 size structure to 17 ps laser pulses and modulated radiation of GaAs and CO2 lasers have been studied. The modulation frequencies up to 10 GHz for GaAs laser and up to 1 GHz for CO2 were attained. The use of small radiation power (1 – 10 mW/cm2 for cw radiation and 10 – 100 nJ/cm2 for pulse radiation) in combination with high sensitive read-out system made possible to avoid any non-linear transient processes caused by an overheating of sample above a critical temperature or S-N switching enhanced by an intense radiation. Responses due to the change of kinetic inductance were believed to be negligible. The only signals observed were caused by a small change of the film resistance either in the resistive state created by a bias current or in the normal state. The data obtained by means of pulse and modulation techniques are in agreement. The responsivity about 1 V/W was measured at 1 GHz modulation frequency both for 0.85 micrometers and 10.6 micrometers wavelengths. The sensitivity of high-Tc fast wideband infrared detector is discussed.
|
