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Title:Growth and characterization of epitaxial metastable (gallium arsenide)(1-x)(silicon(2))(x) alloys and (gallium arsenide)(1-x)(silicon(2))(x)/gallium arsenide strained-layer superlattices
Author(s):Mei, Din-How
Doctoral Committee Chair(s):Greene, Joseph E.
Department / Program:Engineering, Metallurgy
Engineering, Materials Science
Discipline:Engineering, Metallurgy
Engineering, Materials Science
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Metallurgy
Engineering, Materials Science
Abstract:Single-crystal metastable (GaAs)$\sb{\rm 1-x}$(Si$\sb2)\sb{\rm x}$ alloys with x $\leq$ 0.57 have been grown on GaAs(001) using a hybrid sputter deposition technique. Triple-crystal x-ray diffraction studies showed that the full-width at half maximum intensity of alloys with x $\leq$ 0.4 were nearly equal to those of the GaAs substrates ($\approx$30 arc-sec) and that the lattice constants, uncorrected for strain, varied linearly between values for GaAs and Si. Alloys with 0 $\leq$ x $\leq$ 0.20 were shown by cross-sectional and plan-view transmission electron microscopy to be dislocation free. Film/substrate lattice misfit strain in alloys with 0.11 $\leq$ x $\leq$ 0.20 was partially accommodated by the formation of an epitaxial interfacial spinodal zone whose height varied from $\approx$20 to 70 nm. The spinodal region consists of lenticular platelets along the (001) growth direction and a Si-rich-(GaAs)$\sb{\rm 1-x}$(Si$\sb2)\sb{\rm x}$/Si-deficient-(GaAs)$\sb{\rm 1-x}$(Si$\sb2)\sb{\rm x}$ compositional modulation orthogonal to the growth direction. Films with x $\geq$ 0.2 exhibited, together with the interfacial zones, inhomogeneously distributed a/2 $\langle$110$\rangle$-type threading dislocations. Antiphase domains extending in the (001) growth direction with $\{$011$\}$ boundaries in plan-view which annihilated each other with increasing film thickness were observed in alloy films with x $\geq$ 0.25. GaAs overlayer experiments strongly indicated that spinodal decomposition in (GaAs)$\sb{\rm 1-x}$(Si$\sb2)\sb{\rm x}$ is not surface initiated but occurs via a solid state transformation.
A combination of XRD, TEM, XTEM, XPS, and optical reflectance anisotropy studies were carried out to investigate the long-range order transition in (GaAs)$\sb{\rm 1-x}$(Si$\sb2$)$\sb{\rm x}$ alloys. The alloys exhibited a higher critical composition x$\sb{\rm c} \approx$ 0.38, than the previously investigated (III-V)$\sb{\rm 1-x}$(IV$\sb2$)$\sb{\rm x}$ systems (GaAs)$\sb{\rm 1-x}$(Ge$\sb2$)$\sb{\rm x}$ and (GaSb)$\sb{\rm 1-x}$(Ge$\sb2$)$\sb{\rm x}$ for which x$\sb{\rm c}$ = 0.30. The difference was shown to be due to a slight Si group-III sublattice preference, resulting in the normalized (002)/(004) XRD intensity ratios being larger than unity at lower compositions and n-type conduction of the alloy films.
(GaAs)$\sb{\rm 1-x}$(Si$\sb2$)$\sb{\rm x}$/GaAs strained-layer superlattices (SLSs) were used as buffer layers between the GaAs substrates and the bulk alloy layers in order to reduce lattice misfit strain. XTEM examinations of SLS structures with alloy layers having Si concentrations x = 0.12, 0.20, or 0.30 showed that they were dislocation free for layer thicknesses $\leq$300, 30, and 25 nm, respectively. Layer interfaces appeared smooth and abrupt. SLS triple-crystal XRD diffraction patterns, exhibiting up to 17 orders of satellite reflections, were fitted very well, both in the number of superlattice satellite peaks and in the relative peak intensities, by diffraction spectra calculated using a kinematic step model. The excellent fit between measured and calculated spectra indicates that the SLS interfaces are abrupt and that layer thicknesses are uniform. The use of (GaAs)$\sb{\rm 0.7}$(Si$\sb2$)$\sb{0.3}$/GaAs SLS buffer layers allowed the growth of dislocation-free alloy overlayers, exhibiting no evidence of interfacial spinodal decomposition, with x up to 0.3.
Issue Date:1991
Rights Information:Copyright 1991 Mei, Din-How
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9210914
OCLC Identifier:(UMI)AAI9210914

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