Improvement of SNSPD Detection Efficiency by Variation of NbN Chemical Composition

Ever since it has been shown that two-dimensionally constricted superconductors can be used to detect single photons, effort has been invested to optimize such devices for applications. In most cases, the detection efficiency, defining the ratio of counted photons vs. incoming photons and hence the sensitivity of the device, is the most important parameter. However, depending on the applications, other parameters, like the absolute pulse strength or the dark count rate, might be important to adjust. Principally, such a superconducting nanowire single photon detector (SNSPD) consists of a very thin superconducting film, which is patterned into a narrow meandering line. To tune the properties of such devices, the optimization of the geometry and layout of such structures has already been the topic of several investigations within our group [1], [2]. However, the device performance can also be influenced by changing the material properties of the superconducting thin film which provides the basis of the SNSPD.