Electrical properties of Au/ and YBa2Cu3O7−x/SrTi1−yNbyO3 heterojunctions were studied by measuring their capacitance-voltage, current-voltage, and conductance-voltage characteristics. The heterostructures were made by depositing Au or YBa2Cu3O7−x films on SrTi1−yNbyO3 substrates. The results of the capacitance-voltage measurement indicated that there was an interfacial layer having a dielectric constant lower than that of bulk SrTiO3 at the Au/SrTiO3 and YBa2Cu3O7−x/SrTiO3 interfaces. The current-voltage characteristics of the Au/SrTi1−yNbyO3 diodes with substrate Nb concentrations of 0.05 and 0.005 wt. % matched characteristics normally associated Schottky junctions and had a large ideality factor, n, consistent with the low-dielectric-constant interfacial layers. When the carrier concentration of the n-SrTiO3 substrate was 2×1019 cm−3, the Au and YBa2Cu3O7−x junctions showed interfacial-layer tunneling characteristics. The YBa2Cu3O7−x junctions exhibited two peaks in their conductance-voltage relations whose peak structures relies on the superconducting state density in YBa2Cu3O7−x films.
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Yoshida et al. (1991) studied this question.