Temperature dependence of niobium superconducting nanowire single-photon detectors in He-3 cryocooler.

Performances of superconducting nanowire single-photon detectors (SNSPDs) based on low T materials strongly depend on the operating temperatures. We have fabricated infrared-sensitive niobium SNSPDs based on doped niobium (Nb*) films and measured them in He-3 cryocooler. The critical current approaches to the de-pairing current at 0.3 K. Therefore, with the decrease in temperatures, we have observed a monotonous increase of count rate at the wavelength of 1,521 nm and exponential decrease of dark count rate at all bias currents. The possible origin of dark counts for doped Nb devices is also discussed. [ABSTRACT FROM AUTHOR]