Hot electron bolometers

The double side-band receiver noise temperature has been measured for a variety of receivers based on several mixing strategies. An InSb hot-electron bolometer operated as a mixer was found to have a double side-band receiver noise temperature = 300 K at 220 GHz (Blaney, 1980). This corresponds to an NEP = 10 W/ /Hz referred to a predetection bandwidth of 100 GHz. The single frequency performance of mixer-based receivers does not generally match this performance, however (Boucher et al., 1993). 

Whisker contact diodes have much faster response times than InSb hot-electron bolometers and may be used as detectors or mixers. A good discussion of the behavior of near-millimeter band cat-whisker diodes... 

Four different detectors have been used in the spectrometers 1) an InSb 4K, liquid He cooled, hot-electron bolometer, operating from 0.3 to 0.6 THz with an NEP of about 10 W/VHz 2) a gallium doped germanium bolometer, cooled to the lambda point of He, operating from 0.6 to 6.5 THz with an NEP of about 10 W/VHz 3) a similar, but %e cooled bolometer, with a two-orders-of-magnitude smaller NEP and 4) a Ge Ga photoconductor, cooled to 4K, with an NEP of 10 W/VHz, operating from 2.5 to 6.0 THz. 

Hot Electron Bolometer, Putley Detector. Whether it is more appropriate to include the hot electron bolometer and Putley detector in a list of detectors employing photon effects, or to instead list them with thermal effects, is somewhat arbitrary. Both employ photon effects in that incident photons interact with free electrons in a semiconductor. However, they are thermal (as the name bolometer implies) in that the effects are explainable in terms of a change in the effective temperature of the free electrons. Because the interpretation is mainly from the viewpoint of a photon-electron interaction, they are included here in the list of photon effects. 

Nb SIS junctions are very sensitive mixer devices, but only for frequencies below the gap energy of Nb( 700 GHz). Superconducting hot electron bolometers (HEBs) use the electron temperature-dependent resistance in superconducting narrow film strips. The mixer performance of the Nb HEB mixer is promising but the bandwidth, determined by the electron-phonon interaction time, is very narrow (—90 MHz). NbN has a short electron-phonon interaction time, so it is possible to obtain a larger bandwidth of 1 GHz. NbN has a larger gap energy than Nb, so the NbN HEB mixer can be operated over 1 THz. In some studies, preliminary experimental results were achieved (91-94). 

H Ekstrdm, B Karasik, E Kollberg, G Gol tsman, E Gershenzon. 350 GHz NhN hot electron bolometer mixer. Proceedings of the 6th International Symposium on Space Terahertz Technology Pasadena, CA, 1995, pp 269-283. 

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