Size-Selecting Semiconductor Templates for Nano-Scale Spatial Control of Self-Assembled Heterostructures

Technical. This project addresses research toward greater understanding and implementing ar-rangement of materials at shrinking dimensions, and the ability to successfully integrate new ma-terials with better properties or materials that would provide new functionalities. The project aims for advanced processing methods that can organize materials at nano-scale dimensions with precise placement having the necessary quality and reliability, for example, to realize concepts for new types of device structures involving single electron tunneling effects (transistors, mem-ory, quantum cellular automata), quantum computing architectures, and integration of III-V ma-terials with group IV substrates for high-speed channels or optical devices. Self-assembly meth-ods alone can arrange structures at these length scales, but cannot place structures at specific lo-cations. The approach is to combine self assembly with a top-down patterning method to direct growth. The project seeks to create topographic templates made up of uniform and size-selecting features through a 'strain-engineering' mechanism. These templates will then be used to nucleate high quality, crystalline nanostructures at specified locations on substrates by self-assembly methods that would occur on the templates. This is expected to provide a route to creating new structures with an arbitrary lateral arrangement and the potential for combining lattice mis-matched materials with silicon that would not be achievable through thin film growth with high quality. Strained SixGe1-x layers will be grown on silicon substrates that have been locally modi-fied at specific sites using a focused ion beam, resulting in pyramidal pit formation at each site with a characteristic size, dependent on strain. The pit edges will be used to provide four closely spaced nucleation sites. Studies will be done on how the template formation is influenced by various patterning parameters and by kinetics during heteroepitaxial growth using ultra high vac-uum sputtering. Studies will also be done to determine how these templates can be used to influ-ence the growth of dissimilar materials under different kinetic conditions. The growth of lattice-mismatched semiconductors (Ge on Si) as well as other materials such as silicides will be ex-plored. Characterization studies will be done to understand the effects on resulting morphology, crystal/interface structure, composition, and uniformity?items which will influence electrical properties and the potential usefulness for device applications. These studies will also include the effect of very small surface discontinuities, defects, or impurities on nucleation processes in technologically important material systems. Non-Technical. The project addresses fundamental research issues in a topical area of elec-tronic/photonic materials science having technological relevance. In addition to graduate student participation, undergraduates will also be directly involved and gain hands-on experience using advanced research tools. Increasing undergraduate research participation at early stages in their education will be a primary focus, with particular encouragement given to women and minori-ties. This undergraduate research will be leveraged to help promote these activities to local high schools, by demonstrating examples of practical hands-on research they will have the opportu-nity to participate in as engineering students. Connections will be made to industry by providing additional examples to students. Many aspects of this research will also be incorporated into new nanotechnology and electromagnetic properties courses and used as supplemental research pro-jects associated with other courses to integrate research and education more effectively.