A-AXIS ORIENTED YBA2CU3OY THIN-FILMS GROWN ON NOVEL BUFFER LAYERS

Preferable growth conditions for preparing a-axis oriented YBa2Cu3Oy ( YBCO) and PrBa2Cu3Oy(PBCO) thin films on SrTiO3 substrates were invest igated. The structural analysis of thin films deposited at various sub strate temperatures and growth rates revealed that cubic structure fil ms with high crystallinity were grown at relatively low substrate temp eratures in the Y-Ba-Cu-O system and at a high deposition rate in the Pr-Ba-Cu-O system, respectively. Although the a-axis orientation growt h of YBCO was found to be enhanced on the cubic-YBCO film with excelle nt lattice matching with YBCO, a large density of segregated particles was observed both in the cubic-YBCO films and the YBCO films grown on them. The surface morphology of a-axis oriented YBCO thin films was s ignificantly improved by utilizing a cubic-YBCO/cubic-PBCO bilayer buf fer. The surface roughness of the 250 nm thick a-axis oriented YBCO th in film grown on the bilayer buffer was confirmed to be less than 25 n m and the T-c(onset) reached 90 K.