Detection Efficiency of a Spiral-Nanowire Superconducting Single-Photon Detector

We investigate the improvement of detection efficiency by a spiral layout of a Superconducting Nanowire Single-Photon Detector (SNSPD). The design is less susceptible to the critical current reduction due to turns in the nanowire than the classical meander design. Detector samples with different nanowire width from 300 to 100 nm are structured from a 4 nm thick NbN film deposited on sapphire substrates. The critical current IC(4.2 K) for spiral, meander, and simple bridge structures is measured and compared. On the 100 nm wide samples, the detection efficiency is measured in the wavelength range 400-1700 nm and the cut-off wavelength of the hot-spot plateau is determined. In the optical range, the spiral detector reaches a detection efficiency of 27.6%, which is ~1.5 times the value of the meander. In the the infrared range the detection efficiency is more than doubled