Ramp-type junction parameter control by Ga doping of PrBa2Cu3O7-delta barriers

We analyzed the transport of charge carriers across PrBa2Cu3-xGaxO7-delta (PBCGO) barriers as a function of barrier thickness, Ga-doping level, temperature, and bias voltage. It was found that by Ga doping, the normal state resistance (R(n)) of the junctions was systematically increased, while the critical current (I-c) remained constant. We argue that pair transport takes place by direct tunneling, whereas the quasiparticles have access to channels formed by one or more localized states inside the barrier. By Ga doping the I(c)R(n) products were increased, up to 8 mV at 4.2 K for junctions with 8 nm thick PrBa2Cu2.6Ga0.4O7-delta barriers. (C) 1996 American Institute of Physics.