TUNNEL BARRIER GROWTH DYNAMICS OF NB ALOX-AL/NB AND NB/ALNX-AL/NB JOSEPHSON-JUNCTIONS/

The growth of very thin aluminum oxide and aluminum nitride tunnel bar riers on top of an about 7 nm aluminum layer is deduced by measurement s of the reflectivity change of a laser beam due to the decrease of th e aluminum laser thickness. Within the first seconds of the process th ermal aluminum oxide grows much faster than aluminum nitride in a nitr ogen plasma. For both barrier types the reflectivity change can be cor related with the Josephson current density of the finished junctions. In a semi-logarithmic scale the current density versus reflectivity ch ange can be approximated by a straight line up to 20 kA/cm2. High curr ent densities with AlNx seem to be more easily controllable than with AlOx.