|
|
Gershenzon EM, Gershenzon ME, Goltsman GN, Semenov AD, Sergeev AV. Wide-band highspeed Nb and YBaCuO detectors. IEEE Trans Magn. 1991;27(2):2836–9.
Abstract: The physical limitations on the response time and the nature of nonequilibrium detection of radiation were investigated for Nb and YBCO film in a wide spectral range from millimeter to near-infrared wavelengths. In the case of ideal heat removal from the film, the detection mechanism is connected with an electron heating effect which is not selective over a wide spectral interval. For Nb, the dependence of the response time on the electron mean free path l and temperature T is tau varies as T/sup -2/l/sup -1/. The values of detectivity D* and tau are 3*10/sup 11/ W/sup -1/ Hz/sup 1/2/ cm and 5*10/sup -9/ s at T=1.6 K, respectively. For YBCO film the tau value of 1-2 ps at T=77 K was obtained; the NEP value of 3*10/sup -11/ W-Hz/sup -1/2/ can be obtained at T=77 K in the case of the optimal film matching to the radiation.
|
|
|
|
Gershenzon EM, Gol'tsman GN, Gogidze IG, Gusev YP, Elantiev AI, Karasik BS, et al. Millimeter and submillimeter wave range mixer based on electronic heating of superconducting films in the resistive state. Sov Supercond. 1990;3(10):1582–97.
|
|
|
|
Gershenzon EM, Gershenzon ME, Goltsman GN, Lulkin A, Semenov AD, Sergeev AV. Electron-phonon interaction in ultrathin Nb films. Sov Phys JETP. 1990;70(3):505–11.
Abstract: A study was made of the heating of electrons in normal resistive states of superconducting thin Nb films. The directly determined relaxation time of the resistance of a sample and the rise of the electron temperature were used to find the electron-phonon interaction time rep,, The dependence of rep, on the mean free path of electrons re,, a 1-'demonstrated, in agreement with the theoretical predictions, that the contribution of the inelastic scattering of electrons by impurities to the energy relaxation process decreased at low temperatures and the observed temperature dependence rep, a T 2 was due to a modification of the phonon spectrum in thin fllms.
1. Much new information on the electron-phonon interaction time?;,, in thin films of normal metals and superconductors has been published recently. This information has been obtained mainly as a result of two types of measurement. One includes experiments on weak electron localization investigated by the method of quantum interference corrections to the conductivity of disordered conductors, which can be used to find the relaxation time T, of the phase of the electron wave function. In the absence of the scattering of electrons by paramagnetic impurities the relaxation time T, is associated with the most effective process of energy relaxation: T;= TL+ rep;, where T,, is the electronelectron relaxation time. At low temperatures, when the dependence T; a T is exhibited by thin disordered films, the dominant channel is that of the electron-electron relaxation and there is a lower limit to the temperature range in which rep, can be investigated.
|
|
|
|
Gol'tsman GN, Semenov AD, Gousev YP, Zorin MA, Gogidze IG, Gershenzon EM, et al. Sensitive picosecond NbN detector for radiation from millimetre wavelengths to visible light. Supercond Sci Technol. 1991;4(9):453–6.
Abstract: The authors report on the application of a broad-band NbN film detector which has high sensitivity and picosecond response time for detection of radiation from millimetre wavelengths to visible light. From a study of amplitude modulated radiation of backward-wave tubes and picosecond pulses from gas and solid state lasers at wavelengths between 2 mm and 0.53 mu m, they found a detectivity of 1010 W-1 cm Hz-1/2 and a response time of less than 50 ps at T=10 K. The characteristics were provided by using a 150 AA thick NbN film patterned into a structure of micron strips. According to the proposed detection mechanism, namely electron heating, they expect an intrinsic response time of approximately 20 ps at the same temperature.
|
|
|
|
Lindgren M, Zorin MA, Trifonov V, Danerud M, Winkler D, Karasik BS, et al. Optical mixing in a patterned YBa2Cu3O7-δ thin film. Appl Phys Lett. 1994;65(26):3398–400.
Abstract: Mixing of 1.56 µm infrared radiation from two lasers in a high quality YBa2Cu3O7-δ thin film, patterned to parallel strips, was demonstrated. A mixer bandwidth of 18 GHz, limited by the measurement system, was obtained. A model based on nonequilibrium electron heating gives a good fit to the data and predicts an intrinsic mixer bandwidth in excess of 100 GHz, operating in the whole infrared spectrum. Reduction of bolometric effects and ways to decrease the conversion loss of the mixer is discussed. The minimum conversion loss is expected to be ~10 dB.
|
|
|
|
Gousev YP, Gol'tsman GN, Semenov AD, Gershenzon EM, Nebosis RS, Heusinger MA, et al. Broadband ultrafast superconducting NbN detector for electromagnetic radiation. J Appl Phys. 1994;75(7):3695–7.
Abstract: An ultrafast detector that is sensitive to radiation in a broad spectral range from submillimeter waves to visible light is reported. It consists of a structured NbN thin film cooled to a temperature below Tc (∼11 K). Using 20 ps pulses of a GaAs laser, we observed signal pulses with both rise and decay time of about 50 ps. From the analysis of a mixing experiment with submillimeter radiation we estimate an intrinsic response time of the detector of ∼12 ps. The sensitivity was found to be similar for the near‐infrared and submillimeter radiation. Broadband sensitivity and short response time are attributed to a quasiparticle heating effect.
|
|
|
|
Gol'tsman GN, Karasik BS, Okunev OV, Dzardanov AL, Gershenzon EM, Ekstrom H, et al. NbN hot electron superconducting mixers for 100 GHz operation. IEEE Trans Appl Supercond. 1995;5(2):3065–8.
Abstract: 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.
|
|
|
|
Il’in KS, Milostnaya II, Verevkin AA, Gol’tsman GN, Gershenzon EM, Sobolewski R. Ultimate quantum efficiency of a superconducting hot-electron photodetector. Appl Phys Lett. 1998;73(26):3938–40.
Abstract: The quantum efficiency and current and voltage responsivities of fast hot-electron photodetectors, fabricated from superconducting NbN thin films and biased in the resistive state, have been shown to reach values of 340, 220 A/W, and 4×104 V/W,
respectively, for infrared radiation with a wavelength of 0.79 μm. The characteristics of the photodetectors are presented within the general model, based on relaxation processes in the nonequilibrium electron heating of a superconducting thin film. The observed, very high efficiency and sensitivity of the superconductor absorbing the photon are explained by the high multiplication rate of quasiparticles during the avalanche breaking of Cooper pairs.
|
|
|
|
Semenov AD, Hübers H-W, Schubert J, Gol'tsman GN, Elantiev AI, Voronov BM, et al. Design and performance of the lattice-cooled hot-electron terahertz mixer. J Appl Phys. 2000;88(11):6758–67.
Abstract: We present the measurements and the theoreticalmodel of the frequency-dependent noise temperature of a superconductor lattice-cooled hot-electron bolometer mixer in the terahertz frequency range. The increase of the noise temperature with frequency is a cumulative effect of the nonuniform distribution of the high-frequency current in the bolometer and the charge imbalance, which occurs at the edges of the normal domain and at the contacts with normal metal. We show that under optimal operation the fluctuation sensitivity of the mixer is determined by thermodynamic fluctuations of the noise power, whereas at small biases there appears additional noise, which is probably due to the flux flow. We propose the prescription of how to minimize the influence of the current distribution on the mixer performance.
|
|
|
|
Il'in KS, Lindgren M, Currie MA, Semenov D, Gol'tsman GN, Sobolewski R, et al. Picosecond hot-electron energy relaxation in NbN superconducting photodetectors. Appl Phys Lett. 2000;76(19):2752–4.
Abstract: We report time-resolved characterization of superconducting NbN hot-electron photodetectors using an electro-optic sampling method. Our samples were patterned into micron-size microbridges from 3.5-nm-thick NbN films deposited on sapphire substrates. The devices were illuminated with 100 fs optical pulses, and the photoresponse was measured in the ambient temperature range between 2.15 and 10.6 K (superconducting temperature transition TC). The experimental data agreed very well with the nonequilibrium hot-electron, two-temperature model. The quasiparticle thermalization time was ambient temperature independent and was measured to be 6.5 ps. The inelastic electron–phonon scattering time Ï„e–ph tended to decrease with the temperature increase, although its change remained within the experimental error, while the phonon escape time Ï„es decreased almost by a factor of two when the sample was put in direct contact with superfluid helium. Specifically, Ï„e–ph and Ï„es, fitted by the two-temperature model, were equal to 11.6 and 21 ps at 2.15 K, and 10(±2) and 38 ps at 10.5 K, respectively. The obtained value of Ï„e–ph shows that the maximum intermediate frequency bandwidth of NbN hot-electron phonon-cooled mixers operating at TC can reach 16(+4/–3) GHz if one eliminates the bolometric phonon-heating effect.
|
|
