Niobium thin-film Josephson junctions using a semiconductor barrier

Abstract

Thin‐film superconductive tunnel junctions were fabricated using rf‐sputtered germanium or indium antimonide films as barrier layers on photoetched rf‐sputtered niobium patterns with evaporated lead counter electrodes. Tunneling characteristics similar in quality and shape to those of niobium‐oxide‐lead junctions were obtained, large Josephson currents occurring in the higher‐conductance devices. Stability of the characteristics with time was also found to be comparable to oxide junctions. Reducing the thickness of the semiconductor film appears to produce an increase in the effective tunneling barrier energy, and a model is proposed to explain this. This behavior is of importance when considering the relative merits of semiconductor barriers compared to oxide barriers for Josephson junctions.