Fractal Superconducting Nanowire Avalanche Photodetector at 1550 Nm with 60% System Detection Efficiency and 1.05 Polarization Sensitivity

Superconducting nanowire (nanostrip) single-photon detectors (SNSPDs) have shown unprecedented detection efficiency and timing properties, but simultaneously achieving polarization-insensitive high detection efficiency, low dark-count rate (DCR), fast speed, and low timing jitter remains a challenge. Here we report on our design, fabrication, and characterization of a cascaded superconducting avalanche photodetector composed of 40 nm wide NbTiN nanowires patterned into fractal curves. At the base temperature of 2.7 K, the device exhibits 60 ± 3 % system detection efficiency at the wavelength of 1550 nm, 1.05 polarization sensitivity, 220 cps DCR, 4 ns recovery time, and 45 ps timing jitter. This Letter not only demonstrates these combined properties on a single detector that was unobtainable previously, but also shows that that current-crowding effect remarkably permits decent internal detection efficiency. These counter-intuitive results expand the understanding pertaining to the device physics of SNSPDs.