Atomic layer-by-layer MOCVD of oxide superconductors

A very smooth surface film of c-axis oriented YBa 2 Cu 3 Ox (YBCO) with roughness of less than monomolecular layer over 10μmx10μm, free of precipitates, has been obtained by atomic layer-by-layer metalorganic chemical vapor deposition (MOCVD) on a SrTiO 3 substrate at 650°C. A very large terrace length of 0.3-0.5μm may be due to the enhanced migration of growing species on the surface. The result of an attempt to prepare YBCO films with a larger terrace width surface using NdGaO 3 substrates is discussed. The correlation between boulder formation and dislocations in the substrate is clarified and methods for eliminating boulders are proposed. Very high superconductivity critical current densities of 3x10 7 A/cm 2 at 4.2K and 3x10 6 A/cm 2 at 77K have been obtained.