This award will support collaborative research between Dr. Kenneth H. Westmacott and Ulrich Dahmen, National Center for Electron Microscopy, Lawrence Berkeley Laboratory and Dr. J. Y. Laval, Laboratoire des Microstructures, Ecole Superieure de Physique et de Chimie Industrielles, Paris, France. The objective of the research is to study the microstructural characterization of heterostructure strained layer superlattices. An important problem in the fabrication and application of strained-layer superlattices is the effect of misfit-dislocations on their microstructure and electro-optical properties. This problem arises because, depending on the system chosen, the strain developed in the superlattice layers may in some cases exceed the limit of elastic accommodation. In this joint project, heterostructure strained-layer superlattices based on GaAs will be fabricated under closely controlled conditions using molecular beam epitaxy. The resulting films will be examined by atomic resolution electron microscopy to determine the overall film structure, the dislocation and defect character and distribution and the interface structure. Parallel in-situ electrical measurements performed on a specially adapted microscope will relate the microstructure to properties. A fundamental study of the effect of substrate orientation and ledge structure on film quality will be followed by attempts to produce optimized films with superior properties. Both the U.S. and French groups have significant expertise in the proposed research area. The joint project will benefit from access to advanced U.S. electron microscopes, as well as French strengths in molecular beam epitaxy growth of heterointerfaces.
