Structural and Magnetic Characterization of Bi-Substituted Garnet on Si and GaAs
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ABSTRACT Novel material structures that combine magneto-optic (MO) and semiconductor devices have We have potential applications in monolithic microwave systems and optoelectronics. investigated the materials issues pertaining to the film structure, interface uniformity, and magnetic/MO properties of (BiDy) 3(FeGa) 501 2 (Bi-DyIG) thin films sputter deposited on Si and GaAs. The rapid thermally annealed films were polycrystalline with a nominal grain size of 20 nm. The magnetic and MO properties were strongly dependent on the type of substrate such that square hysteresis loops and coercivities of 0.1 to 0.9 kOe were observed for Bi-DyIG/Si structures while Bi-DyIG/GaAs structures showed much lower coercivity values (0.03 kOe). A comparison of the magnetic properties, microstructure and substrate composition was carried out with plan-view and cross-section transmission electron microscopy, as well as electron and x-ray diffraction. The results suggest that grain orientation effects, stress, and compositional inhomogeneity due to interfacial reactions or diffusion introduced by the substrate strongly influence the magnetic and MO properties of the films. INTRODUCTION Monolithic integration of magnetic and magneto-optic (MO) materials with semiconductor electronics and optoelectronics has potential for a host of novel device applications that include microwave electronics [1,2], sensors [3], as well as information storage and processing [4,5]. Combining MO materials with underlying high speed III-V or Si electronic and optoelectronic device structures offers device opportunities that exploit the properties of both materials. In particular, we have investigated the possibility of monolithically combining MO and optoelectronic devices such as lasers and detectors. To realize an integrated device, compromises in growth conditions and materials compatibility may be necessary to ensure that the properties of each material are maintained. Integrating MO materials with lasers, for example, places certain restraints on the MO material selection. These criteria include selecting an MO material with a large Faraday rotation, perpendicular magnetic anisotropy, and low absorption at the wavelength of interest. Bismuth substituted garnets satisfy these criteria [6,7]. These materials exhibit large Faraday rotation of about 1-2 °/gm at 633 nm, when sputter deposited, and more transparency than metal MO films such as TbFe [8]. However, the garnet films are typically deposited in an amorphous, non-magnetic state and require a subsequent high temperature (600-700 'C) anneal to obtain a magnetic, crystalline form [9]. During processing, these temperatures could reduce the integrity of the underlying semiconductor. Furthermore the garnet film properties are sensitive to various 41
Mat. Res. Soc. Symp. Proc. Vol. 384 0 1995 Materials Research Society
growth and processing conditions [9], as well as substrate properties such as lattice constant and thermal expansion coefficient [10]. Hence the figures of merit of both the MO material a
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