(250a) Chemical Vapor Phase Formation of Complex Heterostructures
Thin layer monolithic structures composed of metals, semiconductors, and dielectrics underlie most of our modern electronic and optical devices and systems. Typically these thin films are synthesized through chemical means combined with vapor phase transport. Chemical vapor deposition or CVD is a critical process to form these thin layers. Perhaps most demanding application of these thin film processes is the formation of epitaxial semiconductor heterostructures. Modern epitaxial technologies of metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) allow the cost-effective formation of planar structures, over multiple wafers with incredible precision and reproducibility. In general, the challenges set forth by the new classes of device structures are the lateral and in depth control of composition, the controlled placement of quantum structures, and the use of strain-controlled and driven growth. To accomplish these new materials structures, we require a detailed understanding of the gas phase and surface chemistry active during the thin film formation process. The understanding of these processes is now accessible through advances in experimental techniques allowing in situ characterization and monitoring as well as through the advent of predictive numerical and theoretical approaches to understanding the relevant surface chemistry. This talk will present an overview of these processes and their place in current science and manufacturing. While these processes traditionally have focused on the synthesis of materials that are thermodynamically stable, there is increasing interest in using surface chemical and transport kinetics to allow the formation of materials whose composition lies within a miscibility gap. While these potentially interesting alloys are thermodynamically prohibited, they can be formed by suppressing those surface processes which lead to local phase separation during growth. Recent work on the formation of ternary to pentanary compound semiconductor alloys within their respective compositional miscibility gaps will be presented as examples of the development of materials which can open new areas of device design and technology.