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Verevkin, A. A.; Ptitsina, N. G.; Chulcova, G. M.; Gol'Tsman, G. N.; Gershenzon, E. M.; Yngvesson, K. S. |
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Title |
Determination of the limiting mobility of a two-dimensional electron gas in AlxGa1-xAs/GaAs heterostructures and direct measurement of the energy relaxation time |
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Journal Article |
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1996 |
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Phys. Rev. B Condens. Matter. |
Abbreviated Journal |
Phys. Rev. B Condens. Matter. |
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53 |
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12 |
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R7592-R7595 |
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2DEG, AlGaAs/GaAs heterostructures |
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Abstract ![sorted by Abstract field, descending order (down)](img/sort_desc.gif) |
We present results for a method to measure directly the energy relaxation time (τe) for electrons in a single AlxGa1−xAs/GaAs heterojunction; measurements were performed from 1.6 to 15 K under quasiequilibrium conditions. We find τeαT−1 below 4 K, and τe independent of T above 4 K. We have also measured the energy-loss rate, ⟨Q⟩, by the Shubnikov-de Haas technique, and find ⟨Q⟩α(T3e−T3) for T<~4.2 K; Te is the electron temperature. The values and temperature dependence of τe and ⟨Q⟩ for T<4 K agree with calculations based on piezoelectric and deformation potential acoustic phonon scattering. At 4.2 K, we can also estimate the momentum relaxation time, τm, from our measured τe. This leads to a preliminary estimate of the phonon-limited mobility at 4.2 K of μ=3×107 cm2/Vs (ns=4.2×1011 cm−2), which agrees well with published numerical calculations, as well as with an earlier indirect estimate based on measurements on a sample with much higher mobility. |
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0163-1829 |
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PMID:9982274 |
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1612 |
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Vahtomin, Yuriy B.; Finkel, Matvey I.; Antipov, Sergey V.; Voronov, Boris M.; Smirnov, Konstantin V.; Kaurova, Natalia S.; Drakinski, Vladimir N.; Gol'tsman, Gregogy N. |
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Title |
Gain bandwidth of phonon-cooled HEB mixer made of NbN thin film with MgO buffer layer on Si |
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Conference Article |
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2002 |
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Proc. 13th Int. Symp. Space Terahertz Technol. |
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Proc. 13th Int. Symp. Space Terahertz Technol. |
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259-270 |
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NbN HEB mixers, conversion gain bandwidth |
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Abstract ![sorted by Abstract field, descending order (down)](img/sort_desc.gif) |
We present recently obtained values for gain bandwidth of NbN HEB mixers for different substrates and film thicknesses and for MgO buffer layer on Si at LO frequency of 0.85-1 THz. The maximal bandwidth, 5.2 GHz, was achieved for the device on MgO buffer layer on Si with a 2 nm thick NbN film. Functional devices based on NbN films of such thickness were fabricated for the first time due to an improvement of superconducting properties of NbN film deposited on MgO buffer layer on Si substrate. |
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Cambridge, MA, USA |
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Harvard university |
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Semenov, A. D.; Hübers, Heinz-Wilhelm; Richter, H.; Birk, M.; Krocka, M.; Mair, U.; Vachtomin, Yu. B.; Finkel, M. I.; Antipov, S. V.; Voronov, B. M.; Smirnov, K. V.; Kaurova, N. S.; Drakinski, V. N.; Gol'tsman, G. N. |
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Title |
Superconducting hot-electron bolometer mixer for terahertz heterodyne receivers |
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Journal Article |
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2003 |
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IEEE Trans. Appl. Supercond. |
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13 |
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2 |
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168-171 |
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NbN HEB mixers |
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We present recent results showing the development of superconducting NbN hot-electron bolometer mixer for German receiver for astronomy at terahertz frequencies and terahertz limb sounder. The mixer is incorporated into a planar feed antenna, which has either logarithmic spiral or double-slot configuration, and backed on a silicon lens. The hybrid antenna had almost frequency independent and symmetric radiation pattern slightly broader than expected for a diffraction limited antenna. At 2.5 THz the best 2200 K double side-band receiver noise temperature was achieved across a 1 GHz intermediate frequency bandwidth centred at 1.5 GHz. For this operation regime, a receiver conversion efficiency of -17 dB was directly measured and the loss budget was evaluated. The mixer response was linear at load temperatures smaller than 400 K. Implementation of the MgO buffer layer on Si resulted in an increased 5.2 GHz gain bandwidth. The receiver was tested in the laboratory environment by measuring a methanol emission line at 2.5 THz. |
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343 |
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Semenov, A.; Richter, H.; Hübers, H.-W.; Smirnov, K.; Voronov, B.; Gol'tsman, G. |
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Title |
Development of terahertz superconducting hot-electron bolometer mixers |
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Conference Article |
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2003 |
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Proc. 6th European Conf. Appl. Supercond. |
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Proc. 6th European Conf. Appl. Supercond. |
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181 |
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2960-2965 |
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NbN HEB mixers |
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We present recent results of the development of phonon cooled hot-electron bolometric (HEB) mixers for airborne and balloon borne terahertz heterodyne receivers. Three iomportant issues have been addresses: the quality of NbN films the HEB mixers were made from, the spectral properties of the HEB mixers and the local oscillator power required for optical operation. Studies with an atomic force microscope indicate, that the performance of the HEB mixer might have been effected by the microstructure of the NbN film. Antenna gain and noise temperature were investigated at terahertz frequencies for a HEB embedded in either log-spiral or twin-slot feed antenna. Comparison suggests that at frequencies above 3 THz the spiral feed provides better overall performance. At 1.6 THz, a power of 2.5 µW was required from the local oscillator for optimal operation of the HEB mixer. |
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Sorrento, Italy |
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0750309814, 978-0750309813 |
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1505 |
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Author |
Semenov, Alexei; Richter, Heiko; Smirnov, Konstantin; Voronov, Boris; Gol'tsman, Gregory; Hübers, Heinz-Wilhelm |
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Title |
The development of terahertz superconducting hot-electron bolometric mixers |
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Journal Article |
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Year |
2004 |
Publication |
Supercond. Sci. Technol. |
Abbreviated Journal |
Supercond. Sci. Technol. |
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17 |
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5 |
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436-439 |
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NbN HEB mixers |
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Abstract ![sorted by Abstract field, descending order (down)](img/sort_desc.gif) |
We present recent advances in the development of NbN hot-electron bolometric (HEB) mixers for flying terahertz heterodyne receivers. Three important issues have been addressed: the quality of the source NbN films, the effect of the bolometer size on the spectral properties of different planar feed antennas, and the local oscillator (LO) power required for optimal operation of the mixer. Studies of the NbN films with an atomic force microscope indicated a surface structure that may affect the performance of the smallest mixers. Measured spectral gain and noise temperature suggest that at frequencies above 2.5 THz the spiral feed provides better overall performance than the double-slot feed. Direct measurements of the optimal LO power support earlier estimates made in the framework of the uniform mixer model. |
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357 |
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