Atomic layer-by-layer growth of superconducting Bi-Sr-Ca-Cu-O thin films by molecular beam epitaxy

In situ reflection high-energy electron diffraction (RHEED) is employed to investigate the growth kinetics, and monitor the crystal surface evolution, during plasma-assisted molecular beam epitaxy growth of Bi2Sr2Can-1CunO (BSCCO) compounds. By varying the growth parameters such as operating pressure, substrate temperature, cation flux and shutter opening pulse duration, it is found that the crystal growth front exhibits surface reconstructions with (1 x 1), (2 x 2), c(2 x 2) and (3 x 1) symmetries for the Sr, Ca and Cu species, and a RHEED pattern characteristic of twinning for Bi. Through manipulation of these surface reconstructions, and use of an adapted growth mode, it was possible to achieve a monolayer coverage for each species supplied. For the n = 1,2 and 3 compounds the resulting films exhibit a crystal quality characterised by an X-ray diffraction rocking curve width of 0.03 degrees and an atomic force microscope mean surface roughness of 0.9 nm [over 10 x 10 mum] for 40 nm thick films. (C) 2000 Elsevier Science B.V. All rights reserved.