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Trifonov, A., Tong, C. - Y. E., Blundell, R., Ryabchun, S., & Gol'tsman, G. (2015). Probing the stability of HEB mixers with microwave injection. IEEE Trans. Appl. Supercond., 25(3), 2300404 (1 to 4).
Abstract: Using a microwave probe as a tool, we have performed experiments aimed at understanding the origin of the output-power fluctuations in hot-electron-bolometer (HEB) mixers. We use a probe frequency of 1.5 GHz. The microwave probe picks up impedance changes of the HEB, which are examined upon demodulation of the reflected wave outside the cryostat. This study shows that the HEB mixer operates in two different regimes under a terahertz pump. At a low pumping level, strong pulse modulation is observed, as the device switches between the superconducting state and the normal state at a rate of a few megahertz. When pumped much harder, to approximate the low-noise mixer operating point, residual modulation can still be observed, showing that the HEB mixer is intrinsically unstable even in the resistive state. Based on these observations, we introduced a low-frequency termination to the HEB mixer. By terminating the device in a 50-Ω resistor in the megahertz frequency range, we have been able to improve the output-power Allan time of our HEB receiver by a factor of four to about 10 s for a detection bandwidth of 15 MHz, with a corresponding gain fluctuation of about 0.035%.
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Meledin D., Desmaris V., Ferm S.-E., Fredrixon M., Henke D., Lapkin I., et al. (2008). APEX Band T2: A 1.25 – 1.39 THz Waveguide Balanced HEB Receiver.181–185.
Abstract: A waveguide 1.25–1.39 THz Hot Electron Bolometer (HEB) balanced receiver was successfully developed, characterized and installed at the Atacama Pathfinder EXperiment (APEX) telescope. The receiver employs a quadrature balanced scheme using a waveguide 90-degree 3 dB RF hybrid, HEB mixers and a 180-degree IF hybrid. The HEB mixers are based on ultrathin NbN film deposited on crystalline quartz with a MgO buffer layer. Integrated into the multi-channel APEX facility receiver (SHeFI), the results presented here demonstrate exceptional performance; a receiver noise temperature of 1000 K measured at the telescope at the center of the receiver IF band 2-4 GHz, and at an LO frequency of 1294 GHz. Stability of the receiver is fully in line with the SIS mixer bands of the SHeFI, and gives a spectroscopic Allan time of more than 200 s with a noise bandwidth of 1 MHz.
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Gershenzon, E. M., Il'in, V. A., Litvak-Gorskaya, L. B., & Filonovich, S. R. (1979). Character of submillimeter photoconductivity in n-lnSb. Sov. Phys. JETP, 49(1), 121–128.
Abstract: A comprehensive investigation was made of the submillimeter photoconductivity of n -1nSb in the range of wavelengths L = 0.6-8 mm, magnetic fields H = 0-30 kOe, electric fields E = 0.01-0.5 V/cm, and temperatures T = 1.3-30 K. The kinetics of the photoconductivity processes as a function of T, E; and H is investigated. It is shown that impurity photoconductivity does exist for any degree of compensation of extremely purified n-InSb. Particular attention is paid to the hopping photoconductivity realized in strongly compensated n-1nSb (K > 0.8).
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Elvira, D., Michon, A., Fain, B., Patriarche, G., Beaudoin, G., Robert-Philip, I., et al. (2010). Time-resolved spectroscopy of InAsP/InP(001) quantum dots emitting near 2 μm. Appl. Phys. Lett., 97(13), 131907 (1 to 3).
Abstract: By using superconducting single photon detectors, we perform time-resolved characterization of a small ensemble of InAsP/InP quantum dots grown by metal organic vapor phase epitaxy, emitting at wavelengths between 1.6 and 2.2 μm. We demonstrate that alloying phosphorus with InAs allows to shift the emission wavelength toward higher wavelengths, while keeping the high optical quality of these quantum dots at room temperature, with no decrease in their radiative lifetime. This work was partially supported by Russian Ministry of Science and Education: Federal State Program “Scientific and Educational Cadres of Innovative” state Contract Nos. 02.740.0228, 14.740.11.0343, 14.740.11.0269, and P931, and RFBR Project No. 09-02-12364.
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Larrey, V., Villegier, J. - C., Salez, M., Miletto-Granozio, F., & Karpov, A. (1999). Processing and characterization of high Jc NbN superconducting tunnel junctions for THz analog circuits and RSFQ. IEEE Trans. Appl. Supercond., 9(2), 3216–3219.
Abstract: A generic NbN Superconducting Tunnel Junctions (STJ) technology has been developed using conventional substrates (Si and SOI-SIMOX) for making THz spectrometers including SIS receivers and RSFQ logic gates. NbN/MgO/NbN junctions with area of 1 /spl mu/m/sup 2/, Jc of 10 kA/cm/sup 2/ and low sub-gap leakage current (Vm>25 mV) are currently obtained from room temperature sputtered multilayers followed by a post-annealing at 250/spl deg/C. Using a thin MgO buffer layer deposited underneath the NbN electrodes, ensures lower NbN surface resistance values (Rs=7 /spl mu//spl Omega/) at 10 GHz and 4 K. Epitaxial NbN [100] films on MgO [100] with high gap frequency (1.4 THz) have also been achieved under the same deposition conditions at room temperature. The NbN SIS has shown good I-V photon induced steps when LO pumped at 300 GHz. We have developed an 8 levels Al/NbN multilayer process for making 1.5 THz SIS mixers (including Al antennas) on Si membranes patterned in SOI-SIMOX. Using the planarization techniques developed at the Si-MOS CEA-LETI Facility, we have also demonstrated on the possibility of extending our NbN technology to high level RSFQ circuit integration with 0.5 /spl mu/m/sup 2/ junction area, made on large area substrates (up to 8 inches).
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