LOW DEFECT DENSIRY/ARBITRARY LATTICE CONSTANT HETEROEPITAXIAL LAYERS

Y09-91-061 LOW DEFECT DENSITY/ARBITRARY LATTICE CONSTANT HETEROEPITAXIAL LAYERS of the Invention A multi-layered structure and process for forming it are described, incorporating a single crystal substrate, a plurality of epitaxial layers having graded composition wherein the layers have changing lattice spacings not exceeding about 2 percent per 1000.ANG. of thickness whereby misfit dislocations are formed to relieve strain and then move to the edges of respective layers. The invention overcomes the problem of large numbers of misfit dislocations threading to the surface of the top layer, especially during device processing at at temperatures in a range from 700 to 900 degrees Celsius. Fully relaxed, incommensurate structures having low defect densities are obtained, where arbitrary combinations of materials can be used.