Comparison of hot spot formation in NbC and NbN single photon detectors
We report an experimental investigation of the hot spot evolution in superconducting single photons detectors (SSPDs) made of disordered superconducting materials with different diffusivity and energy down-conversion time: 33-nmthickNbN and 23-nm-thick NbC films. We have demonstrated that in NbC film only 405 nm photons produce sufficiently largehot-spot to trigger a single-photon response. The dependence of detection efficiency on bias current for 405-nm photons in NbC is similar to that for 3400-nm photons in NbN. In NbC large diffusivity and down-conversion time result in 1D critical current suppression profile compared to usual 2D profile in NbN.