THE INFLUENCE OF Al MORPHOLOGY ON QUALITY IN Nb/Al/AlOx/Al/Nb EPITAXIAL BASE LAYER JUNCTIONS

Nb/Al/AlOX/Al/Nb devices with single crystal base electrodes and low subgap current leakage have applications for particle detectors. To increase quality and reproducibilty in these devices, we have sought to characterize and improve the microstructure of the first Al layer, from which a better -quality AlOx barrier can then be formed. Using a liquid nitrogen cooled stage, we have established a temperature range over which it is possible to grow ultra -high purity Al epitaxially upon single -crystal Nb layers. We compared the effect of epitaxial and non-epitaxial layers upon device quality, and the effect of varying the Al deposition temperature and therefore the nucleation rate at the start of Al layer growth. The main factor in improving V-m was the lower Al deposition temperature. We have seen an improvement of 20-30% in V-m values at 4.2K, using single crystal Nb base electrodes, across a range of J(c) from 50 to 9000 A cm(-2).