Large sensitive-area NbN nanowire superconducting single-photon detectors fabricated on single-crystal MgO substrates

We report on the performance of large area NbN nanowire superconducting single-photon detectors (SSPDs). $20×20μm2$ area SSPDs with 80 and $100nm$ linewidths and 50% fill factor were fabricated in $4-nm$-thick NbN films grown on single-crystal MgO substrates. The high quality of the devices was verified by electrical and optical testing and compares favorably to measurements of $10×10μm2$ area SSPDs. Measurements of kinetic inductance versus bias current indicate that the constriction density is low. The fiber-coupled detection efficiency of the devices was 0.4%–3.5% at $100Hz$ dark count rate.