Nb5N6 Buffered Superconducting NbN Nanowire Single-Photon Detector on Si Substrate

Superconducting nanowire single photon detectors (SNSPDs) based on Si substrates have demonstrated excellent performance, such as high efficiency, low dark count rate, short reset time and low timing jitter. But due to the lattice mismatch between NbN and Si substrate, the performance of film is limited. To this end, Nb5N6 layer is fabricated as the buffer layer between the NbN film and Si substrate, and that will reduce the mismatch and optimize superconducting properties of NbN films. The 6nm-thick film with a 65 nm-thick buffer layer shows the zero resistance critical temperature (Tc0) of 13.27 K, which is 5 K higher than that without buffer. Based on the NbN film on the buffered substrate, we fabricated SNSPD devices demonstrate critical current $(\mathrm{I}_{\mathrm{C}})$ of $65 \mu \mathrm{A}$ which is $5 \sim 6$ times higher to the detectors without buffer. Besides, the experiment results prove that the buffer layer reduces the kinetic inductance, which fasten the recovery of nanowire.