Physical properties of novel amorphous superconducting thin film materials for superconducting nanowire single-photon detectors

Amorphous superconducting thin film materials have the advantages of high superconducting uniformity and good optical response sensitivity, which make them ideal materials for fabricating large-area and mid-infrared superconducting nanowire single-photon detectors (SNSPD). In this paper, three series of different amorphous superconducting films are deposited on Si wafers by room-temperature magnetron co-sputtering. For these films, the dependence of their physical properties, i.e. critical temperature <i>T</i><sub>c</sub>, Ginzburg-Landau coherence length <i>ξ</i>(0), normal-state electron diffusion coefficient <i>D</i><sub>e</sub>, magnetic penetration depth <i>λ</i>(0), and superconducting energy gap <i>Δ</i>(0), on film thickness is systematically investigated. Compared with amorphous tungsten silicide (WSi) and molybdenum germanide (MoGe) superconducting thin films, WGe alloys and WSi have similar superconducting properties, including critical temperature and coherence length, slightly lower normal-state electron diffusion coefficient and higher magnetic penetration depth. Compared with MoGe, both WGe and WSi alloys exhibit larger normal-state electron diffusion coefficient and higher magnetic penetration depths. By studying the superconducting properties of three different amorphous thin films, this research provides new material choices and experimental evidence for developing and optimizing the performance of large-area, high-sensitivity superconducting nanowire single-photon detectors.