Effect of composition and oxygen content on the microwave properties of evaporated Y-Ba-Cu-O thin films

Abstract
Thin films of YBa/sub 2/Cu/sub 3/O/sub 7-x/ have been grown by electron beam evaporation of the metals in the presence of atomic oxygen, with small systematic variations in cation composition. Films grown close to the stoichiometric composition or with excess yttrium are smooth while those with excess barium are substantially rougher. The effect of these differences in cation composition on both microwave and dc properties is dominated by the associated large changes in film morphology. This determines the oxygenation state, and hence the electrical properties, of the superconductor both in the as-grown state and after annealing in a furnace or with atomic oxygen. For all films a strong correlation is found between penetration depth, resistivity and c-lattice parameter which all decrease with increasing oxygen content. In our standard growth regime and at higher oxygen contents the films are overdoped and T/sub c/ falls with increasing oxygen content.