Soft x-ray and EUV response of superconducting tunnel junctions: strong deviations from linearity

Abel Poelaert; Alex G. Kozorezov; Anthony J. Peacock; K. Wigmore; Peter Verhoeve; Axel van Dordrecht; Alan Owens; Nicola Rando

doi:10.1117/12.330279

10 November 1998 Soft x-ray and EUV response of superconducting tunnel junctions: strong deviations from linearity

Abel Poelaert, Alex G. Kozorezov, Anthony J. Peacock, K. Wigmore, Peter Verhoeve, Axel van Dordrecht, Alan Owens, Nicola Rando

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Proceedings Volume 3445, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy IX; (1998) https://doi.org/10.1117/12.330279
Event: SPIE's International Symposium on Optical Science, Engineering, and Instrumentation, 1998, San Diego, CA, United States

Abstract

Nb-Al-AlO_x-Al-Nb Superconducting Tunnel Junctions (SJT's) have been extensively investigated by a number of groups as potential next generation high resolution photon detectors for x-ray astronomy. The response of such devices has been studied from EUV to soft x-rays, using highly monochromatic synchrotron radiation. Based on the current understanding of the charge production and tunneling mechanisms in STJ's, it would be expected that at lower energies, the responsivity of the detector would increase as the role of self-recombination of charge carriers into Cooper pairs declines in importance. Here responsivity is simply defined as the measured charge per eV of photon energy deposited in the junction. This trend however was not observed till the lowest energies. Below a threshold energy the responsivity fell, reaching a minimum level, after which it became constant. This minimum level is lower than the responsivity at 6 keV, by a factor up to 5, leading to a clear mismatch between x-ray and EUV performance. This paper summarizes the observations, and presents quantitative explanations for the feature, based on the existence of local traps in the STJ.

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Abel Poelaert, Alex G. Kozorezov, Anthony J. Peacock, K. Wigmore, Peter Verhoeve, Axel van Dordrecht, Alan Owens, and Nicola Rando "Soft x-ray and EUV response of superconducting tunnel junctions: strong deviations from linearity", Proc. SPIE 3445, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy IX, (10 November 1998); https://doi.org/10.1117/12.330279

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