Properties of Epitaxial YBa₂Cu₃O₇/PrBa₂Cu₃O₇ Heterostructures Sputtered at High Oxygen Pressures

Abstract

Epitaxial multilayers of high temperature superconductors and nonsuperconductors with perovskite structure might be a possible basis for SIS-Josephson junctions, superconducting FETs, and other electronic devices in the future. Heteroepitaxial thin films of superconducting YBa₂Cu₃O₇ and semiconducting PrBa₂Cu₃O₇ have been deposited on [001] SrTiO₃ by dc-sputtering at very high oxygen pressures (4 mbar). Films without precipitates and a very smooth surface produced by this method allow a microstructuring below 0.1 µm. The superconducting properties of very thin YBa₂Cu₃O₇ layers (15 – 30 nm) were examined by resistivity and critical current measurements and did not show any degradation due to the proximity of the PrBa₂Cu₃O₇ layers. A critical current density of 2 × 10⁶ A/cm² at 77 K was measured on a 30 nm thick YBa₂Cu₃O₇ thin film covered by an epitaxial PrBa₂Cu₃O₇ layer with a thickness of 100 nm. The influence of CaF₂ and Ag top-layers has also been investigated. The microstructure, interdiffusion, and epitaxy of the heterostructures have been studied by High Resolution Transmission Electron Microscopy (HREM), Rutherford Backscattering Spectroscopy, He-ion channeling and SIMS. The interface between the different layers and at the substrate are crystalline. No interdiffusion at the interfaces between the different layers could be observed. From the contrast change in cross sectional HREM images it can be concluded that the chemical composition across the YBa₂Cu₃O₇/PrBa₂Cu₃O₇ interface changes within one unit cell in c-direction. Because of the very short coherence length in the high temperature superconductors this is an essential condition which has to be fulfilled for the realization of many cryoelectronic devices.

on leave from Institute of Materials Science, Fudan University Shanghai, China

on leave from Universidad del Valle, A.A. 25360 Cali, Columbia