Tunnel Junctions on Chemically Etched YBa 2 Cu 3 O 7 Thin Films
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TUNNEL JUNCTIONS ON CHEMICALLY ETCHED YBa 2 Cu 30 7 THIN FILMS JULIA M. PHILLIPS, J. M. VALLES, JR., A. M. CUCOLO*, R. C. DYNES, M. GURVITCH, J. P. GARNO, AND J. H. MARSHALL AT&T Bell Laboratories, Murray Hill, NJ 07974 *Physics Dept., University of Salerno, 84081 Baronissi, ITALY
ABSTRACT We have prepared low leakage tunnel junctions on epitaxial YBa 2 Cu 3 0 7 (YBCO) films grown on SrTiO 3 (001) by evaporating Pb counterelectrodes onto chemically etched YBCO surfaces. Structure in the voltage dependence of the tunneling conductance is reproducible and strongly resembles what has been obtained in similarly etched junctions on YBCO single crystals.
Surfaces of YBCO thin films which are prepared by a post-growth anneal after removal from the growth chamber suffer from a number of imperfections which are not conducive to surfacesensitive experiments. In addition to non-ideal stoichiometry at the surface, the morphology of such films is rough, and improperly oriented crystallites frequently reside on the surface of even high quality epitaxial films. These defects, coupled with the very short coherence length in YBCO (kc-1-2AL; ab-15A [1]) conspire to make tunneling measurements on untreated post-annealed films unreliable. A number of groups have, however, reported the fabrication of high quality tunnel junctions on smooth films grown by techniques which do not require a post-growth anneal [2]. In order to obtain reproducible tunneling data on post-annealed films, it is clearly necessary to remove the non-superconducting surface layer. It has recently been reported that a chemical etch can remove this layer enabling one to produce tunnel junctions on YBCO single crystals [3]. We have also reported the production of tunnel junctions fabricated by the same method on YBCO thin films [4]. YBCO films were deposited in a vacuum chamber with base pressure
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