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 multistage 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 μm × 15 μm) 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/n² 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.