"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Technical. The goals of this research are to achieve greater understanding of synthesis and processing of new types of crystalline silicon and silicon nanostructures, to characterize their basic electronic and optical properties, and to explore their utility in prototype devices. The silicon in common use is an indirect-bandgap semiconductor with a diamond crystal structure. While there have been significant efforts in searching for materials compatible with current silicon technology and/or materials that could be integrated with silicon for improved performance, this project explores the silicon wurtzite crystal structure; silicon quantum wells (QWs) and superlattices (SLs) made of layers of wurtzite silicon and regular diamond silicon will be studied. Stable wurtzite silicon was prepared 45 years ago using high-pressure indentation. The results of previous experiments and theoretical studies have supported the conclusion that wurtzite silicon has a lower bandgap than diamond silicon, but an accurate knowledge of the wurtzite silicon bandgap is still lacking because of difficulties in material preparation and measurement. This project addresses basic material synthesis, processing, and characterization, as well as prototype device realization. Wurtzite silicon characteristics, such as bandgap and band offset with diamond silicon will be obtained. The project will also utilize nanowires as a platform for the study of new types of crystalline silicon and silicon heterostructures. Because of the lower bandgap of wurtzite silicon and the intimate integration of wurtzite silicon with diamond silicon, new silicon devices may have significantly enhanced performance and functionality. The structure-modulated nanostructures, silicon QWs and SLs, may provide new ways to achieve enhanced optical and electronic properties of silicon and open up new opportunities in basic research and device possibilities. Non-Technical. The project addresses fundamental research issues in a topical area of electronic/photonic materials science having technological relevance. Successful synthesis and demonstration of the new nanostructures and prototype devices could revolutionize the silicon industry to some degree. Results from this project will be disseminated through publications, conference presentations, and the PI's Web site. Research results will also be incorporated into graduate and undergraduate courses that the PI teaches. New types of infrared solar cells based on wurtzite silicon are expected to be one of the term projects for students (graduate students or senior undergraduate students). One or two high school teachers are expected to join the PI's research group during each summer session and to actively participate in research. These teachers will be sponsored by Cullen College of Engineering's Summer Research program for greater Houston high school math and science teachers (www.egr.uh.edu/ret). The program is designed to include 12 bright teachers with enthusiasm for research that is subsequently shared with their respective high school classes during the school year. Teachers will be recruited from the Houston metro area, with at least one half of the participants coming from HISD (the Houston Independent School District). The recruitment plan will yield not only a diverse group of teacher participants but will also impact ethnically and socio-economically diverse students in the participants' high school courses; 38% of HISD students are African American, 58% are Hispanic, and 82% qualify for free or reduced lunch. Because of the diversity of teachers, the training and experiences obtained by teachers is expected to have a broad influence on a diverse body of students, especially minority students. This project will also directly benefit K-12 education. The Greater Houston area is among the largest and most diverse metropolitan areas in the nation. This diversity is reflected in the student body of the Harmony Science Academy, a charter school in Houston (http://hsahouston.org/) with which the PI has established a partnership. Through this partnership, high school students from the academy will spend after-school hours in the PI's lab, working on projects related to nanotechnology and energy. Their research results will be presented in the annual I-SWEEEP conference that will be held at the George R. Brown Convention Center in Houston.
