Atomic-Scale Structure and Surface Kinetics of Semiconductor Heteroepitaxy

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This project explores several key issues related to growth of group IV epitaxial materials by surfactant mediated processes. In situ studies will center on adsorption of elements from groups IV-VI on the (001) surface of Si and Ge single crystals to explore issues of general importance for heteroepitaxy. The approach is to first determine the structure of equilibrium and metastable surface phases of relevant monoelemental adsorbates. Next, adsorption on pseudomorphic layers will be studied to gain an understanding of factors such as lattice strain, steric effects, and relative chemical bond strength that determine the structure of a particular surface heterophase. The modification of the kinetics of surface processes by surfactants will then be explored, and exploited to facilitate growth of metastable epitaxial alloy structures. The structural perfection and lattice strain of the heteroepitaxial thin films produced will be examined as a sensitive monitor of the efficacy of the investigated growth technique. The study features x-ray standing waves, surface x-ray diffraction, and surface extended x-ray absorption fine structure spectroscopy, and focuses on the initial and secondary phases of strained-layer heteroepitaxy, as well as the kinetics of epitaxial growth. Specific aspects of heteroepitaxial growth to be examined are: (1)surface structure resulting from the deposition of a monolayer (or less) of a heterolayer, (2)surface structure of growth-related adsorbates (e.g., surfactants or dopants) on the surface of the substrate, (3)structure found on the surface of a thin strained heterolayer, and (4)alteration of surface kinetics by the presence of a surfactant species.%%%The project addresses basic research issues in a topical area of materials science having technological relevance. An important feature of the project is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***