Crystal Ion-Slicing of Magnetic and Ferroelectric Oxide Films
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*Department of Applied Physics, Columbia University, Street, New York, NY; 10027 "**Departmentof Physics, State University of New York at Albany, Albany, NY, ***Materials Research Laboratory, Pennsylvania State University, University Park, PA 16802
ABSTRACT The epitaxial separation of single-crystal magnetic and ferroelectric oxide films is presented. Ion implantation is used to create a buried damage layer beneath the surface. The high etch-selectivity of this sacrificial layer makes it possible to detach high quality single-crystal films from bulk samples. Magnetic and electrical properties of the films are discussed. INTRODUCTION Bismuth-substituted yttrium iron garnet (Bi-YIG) and lithium niobate (LiNbO3 ) constitute particularly important materials for integrated-photonic device fabrication, because of their strong magneto-optic (Bi-YIG) and electro-optic response (LiNbO 3) characteristics. Magnetic gamets (Bi-YIG) are needed for on-chip thin film optical isolators, while LiNbO 3 is used to fabricate highly efficient electro-optic modulators. However, it has been heretofore impossible to integrate devices of these oxide systems on semiconductor platforms because of the complex high-temperature chemistry, as well as the usual problems of lattice matching, inherent in the growth of mixed oxides on single-crystal semiconductor surfaces. We describe here a novel technique to detach thin films of these oxides from their growth substrates and bond them onto semiconductor platforms. EXPERIMENT Samples The crystal samples used in this study are obtained from epitaxial thin film growth (YIG) and from homogeneous bulk crystals (LiNbO 3). In the case of the former, the samples are obtained from 91tm-thick single-crystal films of yttrium iron garnet grown by liquid-phase epitaxy on a (111 )-oriented gadolinium gallium garnet (GGG). These epitaxial films have a formula unit of Y 3Fe 5 O12, with small amounts of lanthanum to improve lattice matching to the GGG substrate. The magnetization in the yttrium iron garnet is quasi-planar, with striped domains visible under Faraday-contrast microscopy. Three-gin-thick Bi-YIG epitaxial films on GGG are also used to study the effect of ion implantation below the epilayer/substrate interface. The uniaxial growth anisotropy in these samples, typical of bismuth-substituted YIG films, results in the formation of magnetic domains with the magnetization directed normal to the sample surface. The bismuth-substituted epilayers have a formula unit of Bi 0 6 Y2.4F 50 12 , with trace amounts of gallium. The LiNbO 3 samples are z-cut bulk single-crystal wafers, poled along the c-axis. They are fabricated by the Czochralski technique.
475 Mat. Res. Soc. Symp. Proc. Vol. 517 01998 Materials Research Society
Processing Singly-charged helium ions at 3.8 MeV of energy are implanted several microns below the top surface with little residual damage to the near-surface region. The implant dose on all samples is 5 X 1016 ions/cm 2 . The samples are mounted on a 2 in.-diameter water-cooled target hold
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