In situ epitaxial growth of Y₁Ba₂Cu₃O _7-x films by molecular beam epitaxy with an activated oxygen source

Highly oriented, epitaxial Y₁Ba₂Cu₃O _7-x thin films were prepared on MgO(100) by molecular beam epitaxy at a substrate temperature of 550-600°C. The in situ growth was achieved by incorporating reactive oxygen species produced by a remote microwave plasma in a flow-tube reactor. The epitaxial (001) orientation is demonstrated by x-ray diffraction and ion channeling. In situ reflection high-energy electron diffraction showed that a layer-by-layer growth has produced a well-ordered, atomically smooth surface in the as-grown tetragonal phase of an oxygen stoichiometry of 6.2-6.3. A 500°C anneal in 1 atm of O₂ converted the oxygen content to 6.7 to 6.8. Typical superconducting transport properties of an Y₁Ba₂Cu₃O_7-x film 1000 Å thick are ρ(300 K)=325 μΩ cm, ρ(300 K)/ρ(100 K)=2.4, T_c(onset)=92 K, and T_c(R=0)=82 K. The transport J _c at 75 K is 1×10⁵ A/cm², and increases to 1×10⁶ A/cm² at 70 K.