Electrical Characteristics of Superconducting Nanowire Single Photon Detector

By changing the bias scheme of a superconducting nanowire single photon detector (SNSPD), the current-voltage (I-V) characteristics of SNSPDs are extensively studied. Using a quasi-constant-voltage bias, the SNSPD nonlatching property is observed in the low voltage range. When the bias current surpasses the critical current, a thermal relaxation oscillation occurs because of the hotspot´s periodic appearance, growth, and disappearance. This produces a smooth transition in the I- V curve instead of latching. The oscillation frequency is proportional to the voltage of the SNSPD. A linear dependence of the oscillation frequency on the SNSPD voltage is derived from the circuit model of SNSPD electronics, which fits well with the experimental results. The kinetic inductance of the SNSPD is extracted from the fitting as the sole parameter. In the high-voltage range, the I-V curve is deduced from Skocpol, Beasley, and Tinkham´s self-heating hotspot model, which is consistent with the experimental result. By measuring the return current, we obtained a heat transfer coefficient (α) of 0.7-2 × 10⁵ W · m² · K¹ between the nanowire and the substrate.