MOLECULAR-BEAM EPITAXY OF PRECIPITATION FREE HIGH-TEMPERATURE SMBA2CU3O7-DELTA SUPERCONDUCTOR THIN-FILMS WITH SMALL SURFACE-ROUGHNESS

For the preparation of epitaxial SmBa2Cu3O7-delta thin films, an in si tu and non-reactive MBE process has been developed. Our special design of the MBE system considers the necessity of a high oxygen partial pr essure at the substrate position during the deposition to achieve ther modynamical 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 s ubstrate. A computer supported process control system allows a rate st ability of better than 1% accuracy and the control of the substrate te mperature within 1 K using an infrared pyrometer. The films grow in si tu epitaxially on lattice matching substrates as MgO or SrTiO3. The op timal superconducting properties with T(c) almost-equal-to 91 K and j( c)(77 K, B = 0) almost-equal-to 10(6) A/cm2 are obtained during an in situ annealing procedure in 1 bar O2 after the deposition. Within a su bstrate temperature range of 680 +/- 5-degrees-C an optimal surface qu ality of 200 nm thick standard films is achieved. These films show a s urface roughness of less than 5 SmBa2Cu3O7-delta unit cells on a scale of 2 mum X 2 mum.