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Structure and Morphology of Silicon Germanium Thin Films
Single layer silicon and germanium films as well as nominally 50-50 silicon-germanium alloys were deposited on single crystal silicon and germanium (001) and (111) substrates by ultrahigh vacuum chemical vapor deposition. These films spanned the range of + 4 % film-substrate lattice mismatch. A number of experimental characterization techniques, including reflection high energy electron diffraction, atomic force microscopy and transmission electron microscopy were employed to gauge both surface morphology and surface and interface structure. It was found that the minimization of surface energy controls the initial film coverage of the substrate. Subsequently, films deposited in tension (e. g. Si on Ge) reduce the misfit strain through the formation of misfit dislocations, while those in compression (e.g. Ge on Si) are unstable to the formation of surface undulations. Phenomenological models, developed to account for these findings can also provide insight into the design of potential self-assembling quantum confinement structures.
The United States Air Force Palace Knight Program provided financial support for the experimental work.
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