Electrical properties of epitaxial junctions betweenNb:SrTiO3and optimally doped, underdoped, and Zn-dopedYBa2Cu3O7−δ

Abstract

Epitaxial thin films of optimally doped, underdoped, and Zn-doped $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (YBCO) were grown on single crystal (001) $\mathrm{Nb}:\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ substrates by pulsed laser deposition (PLD) and the electrical properties of the corresponding interface junctions were examined. The growth conditions were optimized in each case to get the appropriate crystalline quality of the films as well as the desired normal state and superconducting properties. The films or heterointerfaces were characterized by x-ray diffraction, Rutherford backscattering (RBS) ion channeling spectrometry in normal and oxygen resonance modes, magnetic susceptibility, four probe in-plane resistivity, and the temperature dependent current-voltage $(I\text{\ensuremath{-}}V)$ characteristics. Nonlinear $I\text{\ensuremath{-}}V$ curves (forward and reverse) were obtained in all the cases, revealing some characteristic differences and interesting temperature evolution. These data, when analyzed within the framework of a standard description of transport across the metal-semiconductor (Schottky) interface, suggest lateral intrinsic nanoscale electrical inhomogeneity in the system. Also as compared to the case of optimally doped YBCO a small but definitive lowering of the effective Schottky barrier height ${\ensuremath{\Phi}}_{\mathrm{B}}$ is observed for junctions based on oxygen underdoped and Zn-doped YBCO.