Large-Area Superconducting Nanowire Single-Photon Detector with   Double-Stage Avalanche Structure
  We propose a novel design of superconducting nanowire avalanche photodetectors (SNAPs), which combines the advantages of multi-stage avalanche SNAPs to lower the avalanche current I_AV and that of series-SNAPs to reduce the reset time. As proof of principle, we fabricated 800 devices with large detection area (15 um * 15 um) and five different designs on a single silicon chip for comparison, which include standard SNSPDs, series-3-SNAPs and our modified series-SNAPs with double-stage avalanche structure 2*2-SNAPs, 2*3-SNAPs, and 3*3-SNAPs. The former three types of the detectors demonstrate fully-saturated device detection efficiencies of ~20% while the latter two types are latching at larger bias currents. In addition, the I_AV of 2*2-SNAPs is only 64% of the switching current I_SW that is lower than series-3-SNAPs (74%) and well below that of 4-SNAPs (84%) reported elsewhere. We also measure that the exponential decay times of the detectors are proportional to (1/n)^2 due to the lack of external choke inductors. In particular, the decay time of 3*3-SNAPs is only 0.89 ns compared to the standard SNSPDs' 63.2 ns, showing the potential to attain GHz counting rates. 
Risheng Cheng, Menno Poot, Xiang Guo, Linran Fan and Hong X. Tang
physics.ins-det