Submm heterodyne mixing using NbCN/Nb sis tunnel junctions |
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| Authors: | H van de Stadt J Mees Z Barber M Blamire P Dieleman and Th de Graauw |
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| Institution: | (1) SRON, Laboratory for Space Research, P.O.box 800, 9700 AV Groningen, The Netherlands;(2) Department of Materials Science and Metallurgy, University of Cambridge, Pembroke street, CB2 3Qz Cambridge, UK;(3) Department of Applied Physics and Materials Science Center, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands |
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| Abstract: | We describe heterodyne mixing experiments with NbCN/Nb quasi-particle tunnel junctions at submillimeter wavelengths. In this wavelength range junctions with niobium nitride as superconducting material are promising because of the high gap voltage, about 5.7 mV, as compared to 3 mV for the more commonly used niobium. As a first step towards all-NbN junctions we investigate the development of junctions with a NbN base electrode and a Nb upper electrode. We present results from samples with two different insulating barriers: aluminum oxide and magnesium oxide. Measured noise temperatures range from 500 K at 345 GHz and 1600 K at 482 GHz to 8500 K at 644 GHz. These results are about one order of magnitude worse than the best results obtained with all-Nb junctions. The difference can be attributed partly to the relatively high radio-frequency (rf) losses in NbN films as compared to Nb. Also sensitivity is reduced because of the relatively high leakage current in the sub-gap region of the I-V curve of the junction. |
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