Bias Voltage Dependence of Quasiparticle Recombination in STJ Detectors with Killed Electrode

Superconducting tunnel junction X-rays detectors Ti/Nb/Al/AlO x /Al/Nb/NbN with the Ti/Nb/Al/ killed electrode has been studied under irradiation by X-rays photons of different energies produced by the fluorescence method. The nonlinearity of the STJ-detector response versus photon energy has been studied as a function of the bias voltage. The minimum of the nonlinearity is observed when the tunneling probability P 1 has maximum and the detector signals have shortest rise times. The experimental data were analyzed on the basis of the diffusion model taking into account the quasiparticle self-recombination. The simple approximate expression for the self-recombination contributions to STJ-detector signal was obtained. The nonlinearity of the response depends on the ratios of the recombination constant to the diffusion coefficient R/D and the diffusion length to the initial radius of the quasiparticle distribution Λ/ a 0 and is inverse proportional to the thickness of the electrode.