Epitaxial growth of SrTiO₃/YBa₂Cu₃O _7-x heterostructures by plasma-enhanced metalorganic chemical vapor deposition

We report heteroepitaxial growth of SrTiO₃ on YBa ₂Cu₃O_7-x/LaAlO₃ substrates by plasma-enhanced metalorganic chemical vapor deposition. X-ray diffraction results indicated that SrTiO₃ films were epitaxially grown on a (001) YBa₂Cu₃O_7-x surface with [100] orientation perpendicular to the surface. The film composition, with Sr/Ti molar ratio in the range of 0.9 to 1.1, was determined by Rutherford backscattering spectrometry and energy dispersive spectroscopy. The thickness of the SrTiO ₃ films is 0.1-0.2 μm. The epitaxial growth was further evidenced by high-resolution transmission electron microscopy and selected area diffraction. Atomically abrupt SrTiO₃/YBa₂Cu ₃O_7-x interface and epitaxial growth with [100] _SrTiO3∥[001]_YBa2Cu₃O _7-x were observed in this study. The superconducting transition temperature of the bottom YBa₂Cu₃O_7-x layer, as measured by ac susceptometer, did not significantly degrade after the growth of overlayer SrTiO₃. The capacitance-voltage measurements showed that the dielectric constant of the SrTiO₃ films was as high as 315 at a signal frequency of 100 KHz. The leakage current density through the SrTiO ₃ films is about 1×10^-6 A/cm² at 2-V operation. Data analysis on the current-voltage characteristic indicated that the conduction process is related to bulk-limited Poole-Frenkel emission.