PLANAR-TYPE TUNNEL-JUNCTIONS WITH BI2SR2CACU2O8-TEMPERATURE SUPERCONDUCTING ELECTRODES AND BI2SR2YCU2O8+DELTA ARTIFICIAL BARRIERS(DELTA HIGH)

We performed a detailed study of the structure and transport propertie s of Bi2212/22Y2/2212 planar-type tunnel junctions. Both high-temperat ure superconducting electrodes and semiconducting barriers are highly epitaxial thin films deposited onto SrTiO3 single-crystal (001) substr ates. Deposition of the films was carried out by a high oxygen pressur e de-sputtering technique, which produces high-quality epitaxial thin films, as determined by x-ray diffraction, lattice resolution transmis sion electron microscopy, and Rutherford backscattering. Critical temp eratures for the superconducting electrodes of 85 K were determined by transport measurements (rho and chi versus T). A study of resistivity as a function of temperature of the semiconducting barriers was perfo rmed. Clear quasiparticle tunneling indicating a gap structure at abou t 30-35 mV, a zero-bias peak, as well as linear and flat background at high voltages have been observed. For junctions with very thin barrie rs weak-link-type behavior was observed. An analysis of the I-V curves for these junctions has been made based on the resistively shunted ju nction model. (C) 1998 American Institute of Physics. [S0021-8979(98)0 0516-7]