Spiral growth of YBa2Cu3O7-y thin films by metalorganic chemical vapor deposition using liquid-state sources

Superconducting YBa2Cu3O7-y (YBCO) thin films were prepared on MgO (100) and LaAlO3 (100) substrates by metalorganic chemical vapor deposition (MOCVD) with liquid-state sources. We investigated the surface morphologies of the samples by atomic force microscopy (AFM), Numerous spiral steps accompanied by screw dislocations were observed in the AFM image. These spiral steps are about 12 Angstrom in height, which agrees well with the one-unit cell length along the c-axis of YBCO. Terrace widths of the spiral growth increased significantly as the substrate temperature rose. Furthermore, the supersaturation ratio calculated from the terrace widths changed considerably at the substrate temperature of 750-800 degrees C. This suggested the occurrence of environmental changes at this temperature region and a quasi-liquid layer was present on the growing surface of the films.