Preparation of thin films of YBa2Cu3Ox with a smooth surface by atomic layer MOCVD

We have prepared thin films of c-axis oriented YBa2Cu3Ox (YBCO) with a very smooth surface, roughness of less than a monomolecular layer of YBCO, by atomic layer-by-layer metalorganic chemical vapor deposition (MOCVD) on SrTiO,(100) and NdGaO,(110) substrates. A YBCO film with a large terrace width of 660 nm has been obtained on a NdGaO3(110) substrate. Boulders, mostly consisting of CuOx, have been frequently observed, even on the surface of films prepared by this method, at intervals of a few μm. We have clarified the correlation between boulder formation and dislocations in the substrates by atomic force microscope (AFM) observation of a film surface of YBCO and a SrTiO3 substrate etched by buffered HF solution. We have tried to avoid producing boulder nuclei on dislocations exposed on the substrate surface by changing the usual sequence of source supply, Ba/Cu/Ba/Cu, Y/Cu for 1 cycle, into a new sequence, Ba, Ba/Y/Cu/Cu/Cu, and have successfully prevented the boulders.