W.T. Stacy

Dependence of lattice parameter on composition in substituted yttrium iron garnet epitaxial layers

Abstract The growth of single crystal layers is described for the composition Y 3− x R x Fe 5− y Ga y O 12 (R=Sm or La) on (111) Gd 3 Ga 5 O 12 substrates by liquid phase epitaxy. The reproducibility of the method is presented, the dependence of the distribution coefficients of the substituents on supercooling, and the relation between strain and composition of the layers are discussed. It is concluded that the formation or ordering of vacancies or interstitials, or substitution by impurities such as Pb 2+ of B 3+ , have a negligible effect on the lattice constant.

Strain induced effects in the LPE growth of garnets

Abstract Lattice strains due to the film-substrate lattice misfit and to the incorporation of substituting ions are shown to affect both the rate of growth and the segregation coefficients of solute constituents present during the growth of thin epitaxial layers of substituted iron garnets from PbO-B 2 O 3 fluxes. The previously derived theories are extended to cover the cases in which large amounts of substituents are incorporated and where consequently the mixing entropies and the changes in lattice size cannot be neglected. It is also shown that even with substrate rotation rates of 180 rpm, solute diffusion can produce significant changes in effective segregation coefficients.

Dislocations, facet regions and growth striations in garnet substrates and layers

Abstract The three garnet substrate defects - dislocations, facet regions and striations - are reviewed and discussed. X-ray diffraction topography (both the Lang transmission configuration and the double crystal reflection method) has been used to characterize these defects and to determine the degree to which they are replicated by an epitaxial garnet layer. In contrast to that of dislocations and facet regions, the strain associated with striations is not always transferred to the layer. This is explained in terms of the strain anisotropy of the striations and the tendency of the layer to replicate only those strain components which lie in the plane of the growth interface.

X-ray topographic study of growth sector strains in KDP single crystals

Abstract Potassium dihydrogen phosphate single crystals have been examined by X-ray topographic techniques. The lattice deformation at the boundary between prismatic and pyramidal sectors of growth and its influence on growth kinetics are discussed. In addition, growth bands in the topographs could be readily ascribed to the occurrence of impurity bands.

Helical growth defects in gadolinium gallium garnet

An X-ray topographic study of helical line defects in Czochralski grown Gd3Ga5O12 is described. Both the Lang transmission configuration and the double reflection method have been employed to characterize the strain field in and around the helices. From this study it is concluded that the helix is a dislocation of the prismatic, interstitial type which surrounds a helicoidal region of smaller lattice constant. The topographs also reveal an alignment of the helix loops with the crystal growth striae.

Garnet substrate preparation by homoepitaxy

Abstract The surface preparation of rare earth gallium garnet substrates has been improved by liquid phase homoepitaxy. An examination of the resulting surface by means of X-ray diffraction topography has revealed that the influence of growth striae on the resulting substrate can be reduced by this method.

THERMALLY ACTIVATED STRESS RELIEF IN GARNET LAYERS GROWN BY LIQUID PHASE EPITAXY

The lattice misfit of (Lu, Tb)3Fe5O12 epitaxial layers grown in compression on Gd3Ga5O12 substrates has been found to decrease as a result of annealing at temperatures between 1000 and 1300°C. The deformation rate is thermally activated and depends on the degree of compressive misfit stress at the annealing temperature, the layer thickness and the reducing nature of the anneal atmosphere. Layers which were in tension at the annealing temperature (obtained by using Y3Fe5O12 as the substrate material) did not exhibit stress relief. The process has been found to occur nonhomogeneously by the formation of regions of almost total relief which grow and multiply with continued annealing. The shape symmetry of these regions is consistent with dislocation climb in {112} planes. The results are interpreted in terms of a mechanism involving dislocation climb loops (∽1μm diameter) which develop as a result of the formation of oxygen vacancies.

Dependence of the Uniaxial Magnetic Anisotropy on the Misfit Strain in Gd, Ga:YIG LPE Films

(Gd, Y)3( Fe, Ga)5O‐12 films have been prepared by liquid phase epitaxy on (111) Gd3Ga5O12 substrates at deposition temperatures ranging from 760 to 1010°C. The substrate‐film misfit strain, measured at room temperature, has been found to vary monotonically over this range of deposition temperatures from −23×10−4 to +10×10−4, where the positive sign corresponds to the film being in tension. The uniaxial magnetic anisotropy energy of these films has been studied by measuring both the uniaxial anisotropy field and the magnetization as a function of the misfit strain. Large positive values of the uniaxial anisotropy energy have been measured for films in compression, a result which is contrary to that expected for a negative λ111 and a stress induced anisotropy. Possible explanatory mechanisms involving the misfit strain at the deposition temperature are discussed.

X-ray topographic study of czochralski grown mullite

Abstract Growth striations and dislocation loops in Czochralski grown mullite (2Al 2 O 3 ·SiO 2 ) have been analyzed with X-ray topography. Both the Lang transmission configurations and double crystal reflection method have been employed to characterize the strain field associated with the loops. It is shown to be characteristic of interstitial type loops with segments. parallel to [100], [010], and [110] and Burgers vector parallel to [001].

Interfacial elastic strains in (Al, Ga)As/GaAs heterostructures grown by liquid phase epitaxy

Abstract Double crystal X-ray diffraction topography has been used to analyze localized strains in (Al, Ga)As/GaAs epilayer structures. The strains are caused by a combination of the lattice misfit stress and an unevenness of a given interface. The three major origins of the strains are found to be terracing and meniscus lines in the layer interfaces and pit formation at the substrate surface.