Epitaxial growth and characterization of (110)-oriented YBCO/PBCGO bilayer and YBCO/PBCGO/YBCO trilayer heterostructures

Abstract

We have grown and characterized (110)-oriented YBa2Cu3O7−x (YBCO)/PrBa2(Cu0.8Ga0.2)3O7−x (PBCGO) bilayer and YBCO/PBCGO/YBCO trilayer heterostructures, which were deposited by pulsed laser deposition technique for the nanofabrication of (110)-oriented YBCO-based superconductor (S)/insulator (I)/superconductor (S) tunneling vertical geometry Josephson junction and other superconductor electronic devices. The structural properties of these heterostructures, investigated through various x-ray diffraction techniques (profile, x-ray reflectivity, pole figure, and reciprocal mapping), showed (110)-oriented epitaxial growth with a preferred c-axis-in-plane direction for all layers of the heterostructures. The atomic force microscopy measurement on the top surface of the heterostructures showed crack-free and pinhole-free, compact surface morphology with about a few nanometer root mean square roughness over the 5 × 5 μm2 region. The electrical resistivity measurements on the (110)-direction of the heterostructures showed superconducting critical temperature (Tc) values above 77 K and a very small proximity effect due to the interfacial contact of the superconducting YBCO layers with the PBCGO insulating layer. Raman spectroscopy measurements on the heterostructures showed the softening of the Ag-type Raman modes associated with the apical oxygen O(4) and O(2)-O(3)-in-phase vibrations compared to the stand-alone (110)-oriented PBCGO due to the residual stress and additional two Raman modes at ∼600 and ∼285 cm−1 frequencies due to the disorder at the Cu–O chain site of the PBCGO. The growth process and structural, electrical transport, and Raman spectroscopy characterization of (110)-oriented YBCO/PBCGO bilayer and YBCO/PBCGO/YBCO trilayer heterostructures are discussed in detail.