Molecular beam epitaxy of precipitation free high temperature SmBa 2Cu 3O 7−δ superconductor thin films with small surface roughness

Abstract

For the preparation of epitaxial SmBa 2Cu 3O 7−δ thin films, an in situ and non-reactive MBE process has been developed. Our special design of the MBE system considers the necessity of a high oxygen partial pressure at the substrate position during the deposition to achieve thermodynamical stability of the high- T c -superconductor. The process is based on Knudsen cells for the evaporation of the metallic components and an array of nozzles to introduce molecular oxygen locally to the substrate. A computer supported process control system allows a rate stability of better than 1% accuracy and the control of the substrate temperature within 1 K using an infrared pyrometer. The films grow in situ epitaxially on lattice matching substrates as MgO or SrTiO 3. The optimal superconducting properties with T c ≈ 91 K and j c(77 K, B = 0) ≈ 10 6 A/cm 2 are obtained during an in situ annealing procedure in 1 bar O 2 after the deposition. Within a substrate temperature range of 680±5°C an optimal surface quality of 200 nm thick standard films is achieved. These films show a surface roughness of less than 5 SmBa 2Cu 3O 7−δ unit cells on a scale of 2 μm × 2μm.