Tunneling Measurements on A15 Nb–Si Films

Tunnel junctions have been fabricated on A15 Nb–Si (19–21 at.% Si) films prepared by a dual-target dc-magnetron sputtering method. Nb–Si/oxide/Pb junctions with good tunneling characteristics were obtained using a CF4 cleaning process, in which the Nb–Si base electrode surface was sputter-cleaned in an Ar+CF4 gas mixture prior to oxide barrier formation. Tunneling measurements indicate that Nb-rich A15 Nb–Si is a weak-coupling superconductor, as the same as Nb-rich A15 Nb–Ge and Nb–Al.