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Author Khosropanah, P.; Gao, J. R.; Laauwen, W. M.; Hajenius, M; Klapwijk, T. M.
Title Low noise NbN hot electron bolometer mixer at 4.3 THz Type Journal Article
Year 2007 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.
Volume (down) 91 Issue Pages 221111 (1 to 3)
Keywords NbN HEB mixers, NbN, contacts cleaning
Abstract We have studied the sensitivity of a superconducting NbN hot electron bolometer mixer integrated with a spiral antenna at 4.3 THz. Using hot/cold blackbody loads and a beam splitter all in vacuum, we measured a double sideband receiver noise temperature of 1300 K at the optimum local oscillator (LO) power of 330 nW, which is about 12 times the quantum noise (hnu/2kB). Our result indicates that there is no sign of degradation of the mixing process at the superterahertz frequencies. Moreover, a measurement method is introduced which allows us for an accurate determination of the sensitivity despite LO power fluctuations.
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Call Number Serial 584
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Author Gao, J. R.; Hajenius, M.; Tichelaar, F. D.; Klapwijk, T. M.; Voronov, B.; Grishin, E.; Gol’tsman, G.; Zorman, C. A.; Mehregany, M.
Title Monocrystalline NbN nanofilms on a 3C-SiC∕Si substrate Type Journal Article
Year 2007 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.
Volume (down) 91 Issue 6 Pages 062504 (1 to 3)
Keywords NbN films, nanofilms
Abstract The authors have realized NbN (100) nanofilms on a 3C-SiC (100)/Si(100) substrate by dc reactive magnetron sputtering at 800°C. High-resolution transmission electron microscopy (HRTEM) is used to characterize the films, showing a monocrystalline structure and confirming epitaxial growth on the 3C-SiC layer. A film ranging in thickness from 3.4to4.1nm shows a superconducting transition temperature of 11.8K, which is the highest reported for NbN films of comparable thickness. The NbN nano-films on 3C-SiC offer a promising alternative to improve terahertz detectors. For comparison, NbN nanofilms grown directly on Si substrates are also studied by HRTEM.

The authors acknowledge S. V. Svetchnikov at National Centre for HRTEM at Delft, who prepared the specimens for HRTEM inspections. This work was supported by the EU through RadioNet and INTAS.
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ISSN 0003-6951 ISBN Medium
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Notes Approved no
Call Number Serial 1425
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Author Barends, R.; Hajenius, M.; Gao, J. R.; Klapwijk, T. M.
Title Current-induced vortex unbinding in bolometer mixers Type Journal Article
Year 2005 Publication Applied Physics Letters Abbreviated Journal Appl. Phys. Lett.
Volume (down) 87 Issue Pages 263506 (1 to 3)
Keywords HEB mixer numerical model, HEB model, IV-curves, vortex-antivortex, Berezinskii–Kosterlitz–Thouless theory, diffusion cooling channel, diffusion channel, distributed HEB model, distributed model, self-heating effect, temperature profile
Abstract We present a description of the current-voltage characteristics of hot electron bolometers in terms of the current-dependent intrinsic resistive transition of NbN films. We find that, by including this current dependence, we can correctly predict the complete current-voltage characteristics, showing excellent agreement with measurements for both low and high bias and for small as well as large devices. It is assumed that the current dependence is due to vortex-antivortex unbinding as described in the Berezinskii–Kosterlitz–Thouless theory. The presented approach will be useful in guiding device optimization for noise and bandwidth.
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Notes Approved no
Call Number Serial 604
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Author Baselmans, J. J. A.; Baryshev, A.; Reker, S. F.; Hajenius, M.; Gao, J. R.; Klapwijk, T. M.; Vahtomin, Yu.; Maslennikov, S.; Antipov, S.; Voronov, B.; Gol'tsman, G.
Title Direct detection effect in small volume hot electron bolometer mixers Type Journal Article
Year 2005 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.
Volume (down) 86 Issue 16 Pages 163503 (1 to 3)
Keywords HEB, mixer, direct detection effect
Abstract We measure the direct detection effect in a small volume (0.15μm×1μm×3.5nm)(0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electronbolometermixer at 1.6THz1.6THz. We find that the small signal sensitivity of the receiver is underestimated by 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300K300K and 77K77K. Using a 200GHz200GHzbandpass filter at 4.2K4.2K the direct detection effect virtually disappears. This has important implications for the calibration procedure of these receivers in real telescope systems.
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Call Number Serial 377
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Author Gao, J. R.; Hovenier, J. N.; Yang, Z. Q.; Baselmans, J. J. A.; Baryshev, A.; Hajenius, M.; Klapwijk, T. M.; Adam, A. J. L.; Klaassen, T. O.; Williams, B. S.; Kumar, S.; Hu, Q.; Reno, J. L.
Title Terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer Type Journal Article
Year 2005 Publication Appl. Phys. Lett. Abbreviated Journal Appl. Phys. Lett.
Volume (down) 86 Issue Pages 244104 (1 to 3)
Keywords HEB, QCL
Abstract We report the first demonstration of an all solid-stateheterodyne receiver that can be used for high-resolution spectroscopy above 2THz suitable for space-based observatories. The receiver uses a NbN superconducting hot-electron bolometer as mixer and a quantum cascade laser operating at 2.8THz as local oscillator. We measure a double sideband receiver noise temperature of 1400K at 2.8THz and 4.2K, and find that the free-running QCL has sufficient power stability for a practical receiver, demonstrating an unprecedented combination of sensitivity and stability.
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Notes Approved no
Call Number Serial 905
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