Comparison of Homoepitaxial Growth of YBa2Cu3Oy Films on Variously Oriented YBa2Cu3Oy Single Crystals

Microstructures at interfaces of YBa2Cu3O y (YBCO) thin films homo-epitaxially grown on (001), (100), and (110) oriented YBCO single crystals by RF sputtering and metalorganic chemical vapor deposition (MOCVD) have been studied by transmission electron microscopy. In the case of a (001) YBCO single crystal substrate the orientation of an YBCO thin film grown by RF sputtering depends on the substrate temperature, similar to the case for normal substrates. In the case of a 2° off-cut (001) YBCO substrate grown by MOCVD, no difference of structure between the thin film and the substrate can be distinguished except for a one-unit-cell difference at the interface. When homo-epitaxy is carried out on a (100) YBCO single crystal, a high quality a-axis YBCO thin film can be obtained by either MOCVD or sputtering. Differences in microstructures for (100) and (001) homo-epitaxy are discussed in terms of the layered structure of YBCO as well as differences in growth modes.