High-resolution tunnel junction extreme ultraviolet detectors limited by quasiparticle counting statistics

Superconducting tunnel junctions (STJs) can be used as high-resolution high -count rate photon detectors. They are based on the measurement of the exce ss quasiparticle tunneling current caused by the absorption of a photon in one of the junction electrodes, We have fabricated Nb-Al-AlOx-Al-Nb tunnel junction detectors with different sizes and characterized them in sychrotro n experiments. We present a study of the detector performance in the energy band between 50 and 1000 eV, For photon energies below 70 eV, the intrinsi c device resolution of the best STJ devices agrees with the theoretical lim it set by the statistics of the charge generation and tunneling processes.