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 barriers on top of an about 7 nm aluminum layer is deduced by measurements of the reflectivity change of a laser beam due to the decrease of the aluminum laser thickness. Within the first seconds of the process thermal aluminum oxide grows much faster than aluminum nitride in a nitrogen plasma. For both barrier types the reflectivity change can be correlated with the Josephson current density of the finished junctions. In a semi-logarithmic scale the current density versus reflectivity change can be approximated by a straight line up to 20 kA/cm2. High current densities with AlNx seem to be more easily controllable than with AlOx.