Temperature dependence of the surface morphology of sputtered YBa₂Cu₃O₇ films

A systematic study of the surface morphology of sputtered YBa₂Cu₃O₇ films, as a function of temperature, was performed by means of atomic force microscopy. The investigated films display spiral-shaped islands with a central terrace that is typically much larger than the subsequent terraces. A careful analysis of the observed spirals shows that the change in terrace width occurs within a narrow range of angles. Possible causes for this cross-over, e.g. the role of dislocation stress or the existence of an Ehrlich-Schwoebel barrier, are discussed. Furthermore, the temperature dependences of the central terraces, as well as of the outer terraces, are found to follow an Arrhenius law. These findings are discussed within the framework of a recently developed two-component growth model, where a rate-limiting metallic species (Y, Ba or Cu) is deposited in a reactive gas (in our case O₂). The model indicates that the supersaturation of the components involved is much less than assumed previously.