Effect of the Al thickness on the performance of Nb/Al/AlOx/Al/Nb superconducting tunnel junctions used as x-ray detectors

Nb/Al/AlOx/Al/Nb superconducting tunnel junctions (STJs) have been studied extensively as photon detectors, because of their intrinsic capabilities in terms of charge output and energy resolving power. A critical element in such an STJ is the aluminum layer which separates the superconductive Nb from the AlOx tunnel barrier. In this paper, the role of this Al layer is investigated. The behavior of high quality STJs, differing by the Al thickness only, is analyzed. Five thicknesses ranging between 5 nm and 120 nm are considered. The charge output, the energy linearity and resolution for the case of 6 keV x-ray photons are discussed.

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