Ga segregation in DyBa2Cu3O7-δ/PrBa2Cu3-xGaO7-δ/DyBa2Cu3O7-δ ramp-type Josephson junctions

Ramp-type Josephson junctions with highly doped PrBa2Cu3-xGaxO7-δ barrier layers (x=0.7, 1.0) have been investigated by high-resolution electron microscopy. A Ga-rich intergrowth and Ga diffusion in the ion-milled SrTiO3 substrate are observed. The Ga segregation is responsible for the deviating electrical behavior as expected from extrapolation of low doping levels (x=0.1-0.4). The Ga diffusion in the ion-milled substrate, and possibly in the base electrode, may hamper Josephson junction fabrication using substituted REBa2Cu3O7-δ materials (RE=rare earth