Epitaxial growth of cuprate supersonductors from the gas phase

Abstract

The growth mechanism od c-axis oriented thin epitaxial films of the most widely studied cuprate superconductor YBa2CuO7-δ, formed by a variety of gas phase codeposition methods on common subdstrate materials is described. The evolution of the surface microstructure, as revealed by scanning tunneling miscroscopy (STM), indicates that growth is dominated by the accomodation of depositing species at ledges, which provide energetically favorably positions for this process, lie either along growth spirals emanating from screw dislocations, or when a vicinal substrate is used, separate the low energy (001) planes at the film surface. If the substrate is misoriented sufficiently, growth occurs by step propagation. Otherwise, a high density of screw dislocations ( ≈109 cm-2 is nucleated during the initial stages of growth, providing a continual supply of ledge incorporation sites for the depositing species. Two likely mechanisms for the generation of these screw dislocations are described. The surface evolution reported appears to be an intrinsic feature of c-axis oriented YBa2Cu3O7-δ films for a wide range of growth conditions, irrespective of the substrate material or vapor phase deposition method. © 1994.