Fabrication and Characterization of Superconducting Nanowire Single-Photon Detectors on Si Waveguide

We report the fabrication and characterization of a niobium titanium nitride (NbTiN)-based superconducting nanowire single-photon detector (SSPD or SNSPD) on the Si waveguide toward the realization of waveguide-coupled SSPD. The device consists of a silicon optical waveguide fabricated using a silicon-on-insulator (SOI) substrate and a 100-nm-wide NbTiN nanowire constructed on the waveguide, with an inductor to prevent latch operation. For the fabricated device, the observed superconducting critical temperature and critical current were 7.85 K and 34.4 μA at 0.3 K, respectively. We investigated the optical response of the fabricated device and found that the device exhibited a single-photon response by measuring of the input power dependence of the output count rate. Furthermore, the fabricated device showed a clear bias current dependence of the output counts similar to conventional SSPDs, and the pulse-generation probability is estimated to be 90.1% based on two assumptions: a sigmoidal model to the detection efficiency and the device has a 100% pulse-generation probability at the saturated region.