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

摘要

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 SiOx/Si substrates. The zero-resistance critical temperature (T-C0) maintains a high value of similar to 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/SiOx substrate, with a critical current density (J(C)) of approximately 9.2 x 10(5) A/cm(2) at 2 K. However, there are some differences in the superconducting properties of the ultrathin films on the Si, SiOx/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.