GROWTH AND CHARACTERIZATION OF HIGH-T-C BASED HETEROSTRUCTURES

We have investigated several trilayers based on the Bi2Sr2CaCu2O8+delt a and YBa2Cu3O7+delta families. Our trilayers were realized using Bi2S r2YCu2O8+delta and PrBa2Cu3O7-delta oxide barriers respectively with t hicknesses ranging between 100 Angstrom and 300 Angstrom. The films ha ve been grown on (001) SrTiO3 substrates by means of dc sputtering dep osition in high pressure oxygen plasma. Electrical resistivity measure ments showed T-c = 87 K and 91 K for the Bi2Sr2CaCu2O8+delta and YBa2C u3O7-delta electrodes, respectively, and a semiconductor-like behavior of the Bi2Sr2YCu2O8+delta and PrBa2Cu3O7-delta nonconducting layers. In the case of Cu2O8+delta/Bi2Sr2YCu2O8+delta/Bi2Sr2CaCu2O8+delta junc tions, the tunneling dynamical conductance, G(V), at low temperatures, indicated gap-like structures at +/-30 mV. For the YBa2Cu3O7-delta/Pr Ba2Cu3O7-delta/YBa2Cu3O7-delta junctions, the G(V) showed gap features with very well defined maxima at +/-45 mV and a very low conductance at zero bias. We discuss both these behaviors in close comparison with the results obtained in high-T-c based tunnel structures with natural barriers.