Reactive coevaporation of YBaCuO superconducting films

Growth conditions for YBaCuO thin films are investigated. Films have been made by reactive e-beam coevaporation using three metal sources. In the best cases, as-made films are superconducting with T_c's (R = 0) up to 90 K and J_c's (at 4.2 K) above 10⁷ A/cm². Oxygen pressure, deposition temperature, as well as compositional dependencies of the films are presented. It is found that in conditions of lower oxygen, pressure films with average composition off the 1–2–3 stoichiometry have higher T_c's. For pressure <10 mTorr, the highest T_c obtained is for Ba/Y deposition ratio ⋚1.4. The morphology and impurity phases of these films are examined. The Ba-deficient films have oriented CuYO₂ and CuO as the dominant impurity phases. C-axis lattice parameters (c₀) are also examined. It is found that for a given T_c, films made at lower pressure have c₀'s which are expanded compared to the films made at higher pressures (>100 mTorr). The expanded c₀'s for these films cannot be reduced by a low temperature oxygen anneal. We suggest that metal-atom point-like defects are quenched into these films and we discuss a particular Ba-for-Y substitution model.