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Author |
Hajenius, M.; Yang, Z. Q.; Gao, J. R.; Baselmans, J. J. A.; Klapwijk, T. M.; Voronov, B.; Gol'tsman, G. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Optimized sensitivity of NbN hot electron bolometer mixers by annealing |
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Journal Article |
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Year |
2007 |
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IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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17 |
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2 |
Pages |
399-402 |
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NbN HEB mixers |
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We report that the heterodyne sensitivity of superconducting hot-electron bolometers (HEBs) increases by 25-30% after annealing at 85degC in high vacuum. The devices studied are twin-slot antenna coupled mixers with a small area NbN bridge of 1 mum times 0.15 mum, above which there is a SiO 2 passivation layer. The mixer noise temperature, gain, and resistance versus temperature curve of a HEB before and after annealing are compared and analysed. We show that the annealing reduces the intrinsic noise of the mixer by 37% and makes the superconducting transition of the bridge and the contacts sharper. We argue that the reduction ofthe noise is mainly due to the improvement of the transparency of the contact/film interface. The lowest receiver noise temperature of 700 K is measured at a local oscillator frequency of 1.63 THz and at a bath temperature of 4.2 K. |
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1051-8223 |
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1426 |
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Kitaygorsky, J.; Komissarov, I.; Jukna, A.; Pan, D.; Minaeva, O.; Kaurova, N.; Divochiy, A.; Korneev, A.; Tarkhov, M.; Voronov, B.; Milostnaya, I.; Gol'tsman, G.; Sobolewski, R.R. |
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Title |
Dark counts in nanostructured nbn superconducting single-photon detectors and bridges |
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Journal Article |
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Year |
2007 |
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IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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17 |
Issue |
2 |
Pages |
275-278 |
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SSPD; SNSPD |
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We present our studies on dark counts, observed as transient voltage pulses, in current-biased NbN superconducting single-photon detectors (SSPDs), as well as in ultrathin (~4 nm), submicrometer-width (100 to 500 nm) NbN nanobridges. The duration of these spontaneous voltage pulses varied from 250 ps to 5 ns, depending on the device geometry, with the longest pulses observed in the large kinetic-inductance SSPD structures. Dark counts were measured while the devices were completely isolated (shielded by a metallic enclosure) from the outside world, in a temperature range between 1.5 and 6 K. Evidence shows that in our two-dimensional structures the dark counts are due to the depairing of vortex-antivortex pairs caused by the applied bias current. Our results shed some light on the vortex dynamics in 2D superconductors and, from the applied point of view, on intrinsic performance of nanostructured SSPDs. |
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1051-8223 |
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1248 |
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Ryabchun, S.; Tong, C.-Y. E.; Blundell, R.; Kimberk, R.; Gol'tsman, G. |
![goto web page (via DOI) doi](img/doi.gif)
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Study of the effect of microwave radiation on the operation of HEB mixers in the terahertz frequency range |
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Journal Article |
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Year |
2007 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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17 |
Issue |
2 |
Pages |
391-394 |
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NbN HEB mixers |
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We have investigated the effect of injecting microwave radiation, with a frequency much lower than that corresponding to the energy gap of the superconductor, on the performance of the hot-electron bolometer mixer incorporated into a THz heterodyne receiver. More specifically, we show that exposing the mixer to microwave radiation does not cause a significant rise of the receiver noise temperature and fall of the mixer conversion gain so long as the microwave power is a small fraction of local oscillator power. The injection of a small, but controlled amount of microwave power therefore enables active compensation of local oscillator power and coupling fluctuations which can significantly degrade the gain stability of hot electron bolometer mixer receivers. |
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1051-8223 |
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1427 |
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Semenov, A. D.; Heusinger, M. A.; Renk, K. F.; Menschikov, E.; Sergeev, A. V.; Elant'ev, A. I.; Goghidze, I. G.; Gol'tsman, G. N. |
![goto web page (via DOI) doi](img/doi.gif)
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Title |
Influence of phonon trapping on the performance of NbN kinetic inductance detectors |
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Journal Article |
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Year |
1997 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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7 |
Issue |
2 |
Pages |
3083-3086 |
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NbN KID |
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Voltage and microwave photoresponse of NbN thin films to modulated and pulsed optical radiation reveals, far below the superconducting transition, a response time consistent with the lifetime of nonequilibrium quasiparticles. We show that even in 5 nm thick films at 4.2 K the phonon trapping is significant resulting in a quasiparticle lifetime of a few nanoseconds that is an order of magnitude larger than the recombination time. Values and temperature dependence of the quasiparticle lifetime obey the Bardeen-Cooper-Schrieffer theory and are in quantitative agreement with the electron-phonon relaxation rate determined from the resistive response near the superconducting transition. We discuss a positive effect of the phonon trapping on the performance of kinetic inductance detectors. |
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1598 |
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Svechnikov, S.; Gol'tsman, G.; Voronov, B.; Yagoubov, P.; Cherednichenko, S.; Gershenzon, E.; Belitsky, V.; Ekstrom, H.; Kollberg, E.; Semenov, A.; Gousev, Y.; Renk, K. |
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Title |
Spiral antenna NbN hot-electron bolometer mixer at submm frequencies |
Type |
Journal Article |
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Year |
1997 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
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Volume |
7 |
Issue |
2 |
Pages |
3395-3398 |
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Keywords |
NbN HEB mixers |
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We have studied the phonon-cooled hot-electron bolometer (HEB) as a quasioptical mixer based on a spiral antenna designed for the 0.3-1 THz frequency band and fabricated on sapphire and high resistivity silicon substrates. HEB devices were produced from superconducting 3.5-5 nm thick NbN films with a critical temperature 10-12 K and a critical current density of approximately 10/sup 7/ A/cm/sup 2/ at 4.2 K. For these devices we reached a DSB receiver noise temperature below 1500 K, a total conversion loss of L/sub t/=16 dB in the 500-700 GHz frequency range, an IF bandwidth of 3-4 GHz and an optimal LO absorbed power of /spl sime/4 /spl mu/W. We experimentally analyzed various contributions to the conversion loss and obtained an RF coupling factor of about 5 dB, internal mixer loss of 10 dB and IF mismatch of 1 dB. |
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1051-8223 |
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1597 |
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