Atomic Layer-by-Layer MOCVD of Oxide Superconductors

A very smooth surface film of c-axis oriented Y B a z C w G (YBCO) with roughness of less than monomolecular layer over lOpmxlO~rn, free of precipitates, has been obtained by atomic layer-by-layer metalorganic chemical vapor deposition (MOCVD) on a SrTi03 substrate at 650°C. A very large terrace length of 0.3-0.5pm 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 NdGaOs substrates i s discussed. T h e correlation between boulder formation and dislocations in the substrate is clarified and methods for eliminating boulders are proposed. Very high superconducti\rity critical current densities of 3s10 '~lcm' at 4.2K and 3s10%lcm' at 77K have been obtained.