Effect of Growth Conditions on the Electrical Properties of Nb/AI-Oxide/Nb Tunnel Junctions

We have investigated the dependence of the critical current density Jc of Nb/AIOx/Nb Josephson tunnel junctions on substrate temperature Ts and oxygen exposure E (the product of oxidation time and pressure) during growth. For low O2 exposures, Jc depended sensitively on exposure, Jc ∞ E-16, independent of temperature for 77 K < Ts < 420 K. For high O2 exposures, Jc depended strongly on temperature, with a weaker dependence on exposure: For Ts = 290 K, Jc∞ E-0.4, while for Ts = 77 K, Jc was independent of exposure. © 1995 IEEE