This grant is to purchase the equipment necessary to apply reflection high energy electron diffraction to the study of epitaxial growth of phosphide-based compound semiconductors. The instrument is a charge coupled detector-based camera system which has the capability of high sensitivity and dynamic range, high speed data transfer for real time measurements, multiple beam measurement capacity, high angular resolution. The instrument is being used to study dynamics of dislocations during epitaxial growth of compound semiconductors, the growth of tilted superlattices, surface atomic structure, precision control of stoichiometry, quantum wire devices, and quantum-effect transistors.