Ybco Films and Buffer-Layers Grown In-Situ by Pulsed Laser Deposition
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YBCO FILMS AND BUFFER-LAYERS GROWN IN-SITU BY PULSED LASER DEPOSITION G. A. N. CONNELL*, D. B. FENNER**, D. K. FORK***, J.B. BOYCE*, F.A. PONCE*, F. BRIDGES****, AND T.H. GEBALLE*** *Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304 **Santa Clara University, Santa Clara, CA 95053 ***Stanford University, Stanford, CA 94305 "****Universityof California, Santa Cruz, CA 95064
ABSTRACT YSZ [ (Y2 0 3)x (ZrO2)lx I buffer-layers for various compositions, x, and YBCO (YlBa2Cu307-8) films were grown on hydrogen-terminated Si(100) substrates by laser ablation. The structural and electrical properties of the YBCO are found to depend strongly on x, and to be optimized near x 10.1. INTRODUCTION There have been many attempts to grow YBCO (YlBa 2 Cu 3 07-6) films directly on Si substrates [11 but in all cases the superconducting properties were severely degraded or destroyed throughout a considerable thickness of the film by the reaction of YBCO with Si during growth. With the possible exception of very thick films [2], it therefore appears that high quality YBCO films will only become available on Si through the use of buffer-layers that do not react at elevated temperatures either with YBCO or Si, that grow epitaxially on Si, and that allow for the subsequent epitaxial growth of YBCO. A number of possibilities exist for epitaxial growth on the Si(100) surface, including YSZ [(Y2 0 3)x (ZrO 2)l-x ], the subject of this work[31. It has two ideal properties: first, at temperatures below 720C, the maximum growth temperature used here, reaction with Si and YBCO is minimal [4]; second, for compositions in the range 0.08 < x < 0.4, YSZ grows in the cubic fluorite structure with a lattice constant that closely matches both the near neighbor distance between Si atoms on the (100) surface and the basal plane dimensions in YBCO [5]. We report here a preliminary investigation of this system. We have deposited YSZ buffer-layers as a function of composition, x, followed by YBCO films on hydrogen-terminated Si(100) substrates [61 by laser ablation. We have then correlated the resistivity versus temperature results for YBCO with Xray diffraction (XRD) and transmission electron microscopy (TEM) measurements on both the superconducting and buffer-layers. EXPERIMENTAL METHODS Film deposition is carried out by laser ablation in a PolyGun system[7] in which ten hot-pressed targets are mounted on a rapidly spinning wheel. By synchronizing the pulses from a 308nm XeCl excimer laser with the target wheel rotation, a different sequence of targets may be programmed on each wheel revolution. This feature is used to prepare (Y203)x (ZrO2)l-x by adjusting the ratio of pulses directed at zirconia and yttria targets. Samples with 0 direction normal to the substrate. The work is partially supported by AFOSR !FB, THGI, AT&T iDKF•, and NSF CDBF•. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.
T. Venkatesan, E.W. Chase, X.D. Wu, A. Inam, C.C. Chang, and F. K. Shokoohi, Appl. Phys. Letts. 53,243 (1988); and references therein. P. Berberich, J. Tate
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