Preparation and Characterization of Ultrathin WSi Films for Superconducting Nanowire Single-Photon Detectors

Film quality is the key factor for the performance of superconducting nanowire single-photon detectors with high detection efficiency. Using magnetron cosputtering, high-performance WSi ultrathin films are prepared on MgO (100), Si (100), and SiO _X /Si substrates. The zero-resistance critical temperature (T _C0 ) maintains a high value of ~5 K when the Si content approaches 15%-25% for all three substrates. T _C0 of approximately 3.8 K is obtained for a 4.5-nm-thick WSi film on a Si/SiO _X substrate, with a critical current density (JC) of approximately 9.2 × 10 ⁵ A/cm ² at 2 K. However, there are some differences in the superconducting properties of the ultrathin films on the Si, SiO _X /Si, and MgO substrates. Therefore, we further characterize the structure of the films by X-ray diffraction, transmission electron microscopy, and the angular dependence of the film resistance in different magnetic fields, confirming that the ultrathin WSi films exhibit a preferred orientation rather than an amorphous state.