Thickness dependence of crystalline orientation in YBa_2Cu_3O_x thin films grown by metalorganic chemical vapour deposition

摘要

Reproducible high-quality thin films with uniform and predictable properties are required for electronic device applications. Among the various methods for the fabrication of high-Tc superconducting YBCO thin films, MOCVD is advantageous in the growth of thin films of large area and good uniformity in high oxygen partial pressure [1-3]. The study of the axial growth mechanism of YBCO thin film is important for electronic device applications because of the isotropy of high- Tc superconductors. It is well known that the structure of YBCO thin film grown by physical deposition methods depends on preparation factors such as deposition temperature, oxygen partial pressure, and deposition rate [4-8]. For thicker films, however, Carim et al. [9] reported that the crystalline orientation of YBCO thin film grown by laser ablation depends on the film thickness. They observed that a transition from c-axis normal to the substrate to a-axis normal to the substrate occurs at a thickness of 400 run. Recently, Hamet et al. [10] proposed a model for the mechanism of the transformation between an a-axis oriented film and a c-axis oriented one. In this study, we discuss the thickness dependence of crystalline orientation in YBCO thin films grown on LaAlO3(0 0 1) by MOCVD. This report focuses on the transformation from c-axis to a-axis with increasing film thickness.