Properties of in-Situ Superconducting Y₁Ba₂Cu₃O_7-x Films by Molecular Beam Epitaxy with an Activated Oxygen Source

Abstract

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 a Y₁Ba₂Cu₃O_7-x film 1000Å thick are ρ(300K)= 325 μΩ-cm, ρ(300K)/ρ(100K)= 2.4, T_c(onset) = 92K, and T_c(R=0) = 82K. The transport J_c at 75K is 1×10⁵ A/cm², and increases to 1×10⁶ A/cm² at 70K.