Evaluation of NbTiN Superconducting Strip Photon Detectors With 0.1–30 µm Strip Widths

We report the niobium titanium nitride (NbTiN) superconducting strip photon detectors (SSPDs) with strip widths ranging from 0.1 to 30 µm. The bias current dependences of the detection efficiencies at the 1550 nm wavelength and the dark count rates were systematically evaluated in the wide range of the strip widths. Single-photon detection was confirmed and a saturation trend in the bias current dependence of detection efficiency was also observed for all strip width SSPDs. In addition, we measured the physical properties of the NbTiN films and found the switching current of SSPDs gradually deviated lower from the estimated depairing current with increasing the strip width. Furthermore, the dark counts occurred at the lower bias current relative to the depairing current as the strip width increased. These results suggest that the bias current is unevenly distributed as the strip width increases and the concentrated bias current may induce the dark counts. Our results would provide valuable insights into a better understanding of SSPDs with a wide range of strip widths, the origin of dark counts, and the mechanism of photon detection in superconducting strip.