Nanoscale Structure of Semiconductor Surfaces, Alloys, and Heterostructures

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This project addresses nanoscale geometric and electronic structure of semiconductor surfaces and interfaces. Particular focus is placed on the formation and properties of semiconductor alloys, including both ternary, e.g. In x Ga 1-x N, and quaternary, e.g. In x Ga 1-x As y P 1-y , materials. Incorporation of alloy constituents during growth will be studied, together with the phenomena of atomic ordering, short-range clustering, and long-range alloy compositional fluctuations (lateral composition modulation). The effect of external perturbations such as ion implantation and annealing on the compositional variations will also be examined. Heterostructures, containing layers of material with varying lattice constant, will be used to impose strain on the material. The effect of this strain on the resultant alloy composition and surface morphology will be observed. The intent of the research is to elucidate the underlying microscopic mechanisms responsible for the observed structural or compositional variations, with the aim of designing improved growth and/or processing techniques by which these mechanisms can be controlled. The major technique to be used for these studies is scanning tunneling microscopy (STM), which provides nanoscale information on the atomic arrangement on a surface. Spectroscopic studies with the tunneling microscope will be used to probe electronic states at the surface. Studies will be performed both in a plan-view mode, probing in situ the growth surface of films, as well as in cross-sectional mode in which a heterostructure is cleaved in situ. %%%The project addresses basic research issues in a topical area of materials science having high potential technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new understanding and capabilities in electronic/photonic devices. A variety of fundamental issues are to be addressed in these investigations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area. ***