The Effect of X-Ray Irradiating Superconducting Tunnel Junctions on<tex>$rm Al_2rm O_3$</tex>and<tex>$rm LiNbO_3$</tex>Substrates

Abstract

We have developed a phononmediated radiation detector using Nb-based superconducting tunnel junctions (STJs). The STJs are fabricated on a substrate as an absorber of the radiation, and a substantial amount of emergent phonons with an energy above the energy gap are detected. The performance of the detector depends on the collection efficiency of the phonons. A selection of an appropriate substrate is required for optimizing the detector performance. We fabricated Nb-based STJs on a Al 2 O 3 and a LiNbO 3 substrates, and compared the pulse heights of substrate phonon events due to X-ray irradiation to the substrates. We found that the maximum pulse height of the phonon events for the LiNbO 3 substrate was about twice of that for the Al 2 O 3 substrate, so that these spectra which was obtained from two STJs showed different shapes, especially the peak due to phonon events.