Epitaxial growth of Bi-Sr-Ca-Cu-O superconducting thin films by metalorganic chemical vapor deposition

Abstract

The epitaxial growth of Bi-Sr-Ca-Cu-O thin films was achieved by metalorganic chemical vapor deposition. The film-MgO substrate interface has been examined and discussed using the cross-sectional transmission electron microscopy. On the smooth surface of the MgO substrate, the lattice of the film was ordered from the first atomic layer on the surface of the substrate, and the misfit dislocations caused by the large lattice mismatch between the film and the MgO substrate appeared every four or five lattices. The first Bi2O2 layer on the substrate surface was found to be regularly arranged regardless of the roughness of the substrate surface. The x-ray diffraction patterns of the films as a function of the growth time showed that the high Tc phase (Bi2Sr2Ca2Cu3Ox) was not formed in the early stage of the growth while its amount increased as the growth was prolonged. These results suggest that the high Tc phase is not directly grown but formed via the low Tc phase (Bi2Sr2CaCu2Ox) or semiconducting phase (Bi2Sr2CuOx) with the thermal diffusion limited growth of Cu-O and Ca layers. Even an 8-nm-thick film was found to be free of the compressive stress forming misfit dislocations observed in the transmission electron microscope photograph of the thicker film, since the length of the c axis in the 8-nm-thick film is not enlarged from the result of the x-ray diffraction pattern.