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Author (up) Antipov, S.; Trifonov, A.; Krause, S.; Meledin, D.; Desmaris, V.; Belitsky, V.; Gol’tsman, G. openurl 
  Title Gain bandwidth of NbN HEB mixers on GaN buffer layer operating at 2 THz local oscillator frequency Type Conference Article
  Year 2017 Publication Proc. 28th Int. Symp. Space Terahertz Technol. Abbreviated Journal Proc. 28th Int. Symp. Space Terahertz Technol.  
  Volume Issue Pages 147-148  
  Keywords NbN HEB mixers, GaN buffer-layer, IF bandwidth  
  Abstract In this paper, we present IF bandwidth measurement results of NbN HEB mixers, which are employing NbN thin films grown on a GaN buffer-layer. The HEB mixers were operated in the heterodyne regime at a bath temperature of approximately 4.5 K and with a local oscillator operating at a frequency of 2 THz. A quantum cascade laser served as the local oscillator and a reference synthesizer based on a BWO generator (130-160 GHz) and a semiconductor superlattice (SSL) frequency multiplier was used as a signal source. By changing the LO frequency it was possible to record the IF response or gain bandwidth of the HEB with a spectrum analyzer at the operation point, which yielded lowest noise temperature. The gain bandwidth that was recorded in the heterodyne regime at 2 THz amounts to approximately 5 GHz and coincides well with a measurement that has been performed at elevated bath temperatures and lower LO frequency of 140 GHz. These findings strongly support that by using a GaN buffer-layer the phonon escape time of NbN HEBs can be significantly lower as compared to e.g. Si substrate, thus, providing higher gain bandwidth.  
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  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1175  
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Author (up) Antipov, S.; Trifonov, A.; Krause, S.; Meledin, D.; Kaurova, N.; Rudzinski, M.; Desmaris, V.; Belitsky, V.; Goltsman, G. url  doi
openurl 
  Title Improved bandwidth of a 2 THz hot-electron bolometer heterodyne mixer fabricated on sapphire with a GaN buffer layer Type Journal Article
  Year 2019 Publication Supercond. Sci. Technol. Abbreviated Journal Supercond. Sci. Technol.  
  Volume 32 Issue 7 Pages 075003  
  Keywords NbN HEB mixer, GaN buffer layer, sapphire substrate  
  Abstract We report on the signal-to-noise and gain bandwidth of a niobium nitride (NbN) hot-electron bolometer (HEB) mixer at 2 THz fabricated on a sapphire substrate with a GaN buffer layer. Two mixers with different DC properties and geometrical dimensions were studied and they demonstrated very close bandwidth performance. The signal-to-noise bandwidth is increased to 8 GHz in comparison to the previous results, obtained without a buffer-layer. The data were taken in a quasi-optical system with the use of the signal-to-noise method, which is close to the signal levels used in actual astrophysical observations. We find an increase of the gain bandwidth to 5 GHz. The results indicate that prior results obtained on a substrate of crystalline GaN can also be obtained on a conventional sapphire substrate with a few micron MOCVD-deposited GaN buffer-layer.  
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  Publisher IOP Publishing Place of Publication Editor  
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  Area Expedition Conference  
  Notes Approved no  
  Call Number Antipov_2019 Serial 1277  
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Author (up) Krause, S.; Mityashkin, V.; Antipov, S.; Gol'tsman, G.; Meledin, D.; Desmaris, V.; Belitsky, V.; Rudzinski, M. url  openurl
  Title Study of IF bandwidth of NbN hot electron bolometers on GaN buffer layer using a direct measurement method Type Conference Article
  Year 2016 Publication Proc. 27th Int. Symp. Space Terahertz Technol. Abbreviated Journal  
  Volume Issue Pages 30-32  
  Keywords NbN HEB, GaN buffer layer  
  Abstract In this paper, we present a reliable measurement method to study the influence of the GaN buffer layer on phonon-escape time in comparison with commonly used Si substrates and, in consequence, on the IF bandwidth of HEBs. One of the key aspects is to operate the HEB mixer at elevated bath temperatures close to the critical temperature of the NbN ultra-thin film, where contributions from electron-phonon processes and self-heating effects are relatively small, therefore IF roll-off will be governed by the phonon-escape.Two independent experiments were performed at GARD and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. The entire IF chain was characterized by S-parameter measurements. We compared the measurement results of epitaxial NbN grown onto GaN buffer-layer with Tc of 12.5 K (4.5nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5K (5nm) and observed a strong indication of an enhancement of phonon escape to the substrate by a factor of two for the NbN/GaN material combination.  
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  Notes Approved no  
  Call Number Serial 1202  
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Author (up) Krause, S.; Mityashkin, V.; Antipov, S.; Gol’tsman, G.; Meledin, D.; Desmaris, V.; Belitsky, V.; Rudziński, M. url  doi
openurl 
  Title Reduction of phonon escape time for nbn hot electron bolometers by using gan buffer layers Type Journal Article
  Year 2017 Publication IEEE Trans. Terahertz Sci. Technol. Abbreviated Journal IEEE Trans. Terahertz Sci. Technol.  
  Volume 7 Issue 1 Pages 53-59  
  Keywords NbN HEB mixer  
  Abstract In this paper, we investigated the influence of the GaN buffer layer on the phonon escape time of phonon-cooled hot electron bolometers (HEBs) based on NbN material and compared our findings to conventionally employed Si substrate. The presented experimental setup and operation of the HEB close to the critical temperature of the NbN film allowed for the extraction of phonon escape time in a simplified manner. Two independent experiments were performed at GARD/Chalmers and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. By fitting the normalized IF measurement data to the heat balance equations, the escape time as a fitting parameter has been deduced and amounts to 45 ps for the HEB based on Si substrate as in contrast to a significantly reduced escape time of 18 ps for the HEB utilizing the GaN buffer layer under the assumption that no additional electron diffusion has taken place. This study indicates a high phonon transmissivity of the NbN-to-GaN interface and a prospective increase of IF bandwidth for HEB made of NbN on GaN buffer layers, which is desirable for future THz HEB heterodyne receivers.  
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  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 2156-3446 ISBN Medium  
  Area Expedition Conference  
  Notes Approved no  
  Call Number Serial 1330  
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