High-resolution electron microscopy of epitaxial YBCO/Y 2 O 3 /YSZ on Si(001)
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High-resolution electron microscopy of epitaxial YBCO/Y2O3/YSZ on Si(OOl) A. Bardal Siemens Research Laboratories, Otto Hahn Ring 6, 8000 Munich 83, Germany and SINTEF Applied Physics, 7034 Trondheim, Norway
O. Eibl Siemens Research Laboratories, Otto Hahn Ring 6, 8000 Munich 83, Germany
Th. Matthee, G. Friedl, and J. Wecker Siemens Research Laboratories, 8520 Erlangen, Germany (Received 29 January 1993; accepted 26 April 1993)
The microstructures of YBa 2 Cu 3 07_ 5 (YBCO) thin films grown on Si with Y-stabilized ZrO 2 (YSZ) and Y 2 O 3 buffer layers were characterized by means of high-resolution electron microscopy. At the Si-YSZ interface, a 2.5 nm thick layer of regrown amorphous SiO* is present. The layer is interrupted by crystalline regions, typically 5 to 10 nm wide and 10 to 50 nm apart. Close to the crystalline regions, {111} defects are present in the Si substrate. The typical defect observed is an extrinsic stacking fault plus a perfect dislocation close to the stacking fault which terminates extra {111} planes in the upper part of the Si. These defects are probably formed by condensation of Si self-interstitials created during oxide regrowth. Precipitates are present in the Si close to the Si-YSZ interface and indicate that in-diffusion of Zr has occurred. The YSZ-Y 2 O 3 interface is atomically sharp and essentially planar and contains no second phases. Perfect misfit dislocations with Burgers vector 1/2(110) are present at this interface along with unrelaxed elastic misfit stresses. The Y 2 O 3 -YBCO interface is atomically sharp and planar, but contains steps. (001) stacking faults are present in the YBCO above these steps; the faults are, however, healed a few unit cells away from the interface. By HREM analysis of ultrathin specimen areas, the atomic layer of the YBCO closest to the Y 2 O 3 was found to be a barium-oxygen layer.
I. INTRODUCTION Great effort has been put into the attempts to grow high Tc superconducting films, mainly of YBa 2 Cu 3 07-g (YBCO), on substrates of materials used in microelectronics, such as silicon and gallium arsenide. To obtain epitaxial superconducting films on these substrates for potential applications as superconductorsemiconductor hybrid devices, 12 it is essential to use buffer layers between the substrate and the film, to avoid interdiffusion and interfacial reactions. With a proper choice of buffer layer material, high Tc superconducting films exhibiting high critical temperatures (Tc) and high critical current densities (/ c ) have been grown. Recently, for the YBCO-MgO-GaAs system, Jc = 1.2- 106 A/cm 2 (at T = 77 K) and Tc = 87 K were reported.3 For YBCO films grown on Si substrates, the buffer layer material that has drawn the most attention is yttrium-stabilized zirconia (YSZ), for which critical current densities above 2 • 106 A/cm 2 (at T = 77 K) and critical temperatures of 86—88 K have been reported.4 However, there is an interfacial reaction taking place at the YBCO-YSZ interface5 and a few nm thick layer 2112 http://journals.cambridge.org
J. Ma
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