Characterization of ramp-type Josephson junctions with a Co-doped PrBaCuO barrier

Current transport mechanism in Go-doped PrBaCuO barriers was investigated for ramp-type junctions. The junction characteristics were extremely sensitive to a slight variation in the substrate temperature and the oxygen atmosphere during the heating process for the subsequent barrier layer deposition. Such sensitivity was related to the thermodynamic stability of YBaCuO. The conductance of junctions fabricated under the optimized conditions exhibited an exponential dependence on the barrier layer thickness at low temperatures, and the decay length was estimated to be around 1 nm. Characteristic power law dependence of junction conductance on temperature was confirmed for these junctions, indicating that resonant tunneling and hopping conduction via a small number of localized states were predominant. Clear Josephson characteristics were observed for junctions with a barrier thinner than 11 nm. We found that the experimental I/sub c/ versus barrier thickness relation was also explained well by resonant tunneling models.