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Floet D. W., Gao J. R., Klapwijk T. M., de Korte P. A. J. Bias Dependence of the Thermal Time Constant in Nb Superconducting Diffusion-Cooled HEB Mixers. Appl Phys Lett. 2000;77:1719.
Abstract: We present an experimental study of the intermediate frequency bandwidth of a Nb diffusion-cooled hot-electron bolometer mixer for different bias voltages. The measurements show that the bandwidth increases with increasing voltage. Analysis of the data reveals that this effect is mainly caused by a decrease of the intrinsic thermal time of the mixer and that the effect of electrothermal feedback through the intermediate frequency circuit is small. The results are understood using a qualitative model, which takes into account the different effective diffusion constants in the normal and superconducting domains.
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Semenov AD, Gol’tsman GN. Nonthermal mixing mechanism in a diffusion-cooled hot-electron detector. J Appl Phys. 2000;87(1):502–10.
Abstract: We present an analysis of a diffusion-cooled hot-electron detector fabricated from clean superconducting material with low transition temperature. The distinctive feature of a clean material, i.e., material with large electron mean free path, is a relatively weak inelastic electron scattering that is not sufficient for the establishment of an elevated thermodynamic electron temperature when the detector is subjected to irradiation. We propose an athermal model of a diffusion-cooled detector that relies on suppression of the superconducting energy gap by the actual dynamic distribution of excess quasiparticles. The resistive state of the device is caused by the electric field penetrating into the superconducting bridge from metal contacts. The dependence of the penetration length on the energy gap delivers the detection mechanism. The sources of the electric noise are equilibrium fluctuations of the number of thermal quasiparticles and frequency dependent shot noise. Using material parameters typical for A1, we evaluate performance of the device in the heterodyne regime at terahertz frequencies. Estimates show that the mixer may have a noise temperature of a few quantum limits and a bandwidth of a few tens of GHz, while the required local oscillator power is in the μW range due to ineffective suppression of the energy gap by quasiparticles with high energies.
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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.
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Kardashev NS, Andreyanov VV, Buyakas VI, Vinogradov IS, Gvamichava AS, Kotik AI, et al. The Millimetron project. In: Proc. Lebedev Phys. Institute. Vol 228.; 2000.
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Кардашев НС, Андреянов ВВ, Буякас ВИ, Виноградов ИС, Гвамичева АС, Котик АИ, et al. Проект Миллиметрон. Труды ФИАН им. Лебедева. 2000;228.
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