This CAREER award supports computational and theoretical research that aims to develop a theoretical framework for epitaxial-oxide-semiconductor nanosystems and education in computational materials research targeted on undergraduate and high-school students. Crystalline epitaxial oxides on semiconductors (COS) open a new avenue for complementary metal oxide semiconductor (CMOS) technology utilizing materials other than Si, e.g. Ge or GaAs. Other applications of COS are at the end of the Si technology roadmap; the main advantage of a crystalline oxide is its epitaxial registry to the Si substrate that results in superior device performance by eliminating interfacial defects. COS combined with recently discovered epitaxial semiconductors on oxides (SOX) provides another set of exciting possibilities to explore. The PI aims to develop a comprehensive theoretical framework for the emerging field of nanoscale epitaxial oxide semiconductor systems. The research focuses on fundamental problems in two areas: 1. Crystal growth of oxide-semiconductor and semiconductor-oxide systems. 2. "Tunability" of the electronic and transport properties of epitaxial oxide-semiconductor nanosystems. The key to successful oxide-semiconductor heteroepitaxy is to achieve two-dimensional or Frank-Van der Merwe growth. In addition to lattice and thermal mismatch, the transition between fundamentally different types of bonding across the interface must be considered. The PI will investigate the use of intermetallic Zintl compounds as transition layers between ionic oxides and covalent semiconductors. The central idea is to exploit the intrinsic charge transfer in a Zintl compound to force the more electronegative metal to assume semi-covalent bonding which continues into the semiconductor. Two other key problems are the 90 twin domains caused by breaking of the symmetry across the interfaces (e.g. zinc-blende to perovskite), and step incommensurability between two materials. Relating the atomic geometry and electronic structure of the nanoassembly to its electrical properties, such as charge transfer and retention, will enable the PI to assess possible applications of these systems. The approach is based on ab-initio total energy methods and atomic-scale electron transport techniques that the PI has recently developed. The work will entail close collaboration with experimentalists in academia and industry. To bring the excitement of practical theoretical nanoscience into undergraduate education, the PI plans to develop, improve, and enhance a new course entitled "Practicum on Computational Materials for Nanotechnology." This course will be offered to senior year students in Physics, Chemistry, Electrical Engineering, and Chemical Engineering. An outreach program aimed at attracting female high-school students to nanoscience will also be developed in collaboration with the Physics instructor at the LBJ Science Academy, a magnet high school with a large number of minority students. The PI aims to create an opportunity for female students to spend summers with the PI's research group to learn about computational nanoscience. This activity will be coordinated with a successful existing UTEACH program at UT.
NON-TECHNICAL SUMMARY: This CAREER award supports computational and theoretical research that aims to develop a theoretical understanding of nanosystems and structures on semiconductor surfaces and education in computational materials research with a focus on undergraduates. The PI will use advanced computational tools that start from the constituent atoms to study how oxide materials can be grown on the surfaces of semiconductors, with an emphasis on materials other than silicon, the current workhorse of the electronics industry. The PI will also study the electronic properties of the resulting nanosystems. The PI will focus on fundamental materials science and surface science problems. The work helps lay the theoretical foundations for semiconductor electronic devices with significantly higher performance and enhanced functionality as compared to current electronic device technology. The PI will also explore new phenomena that may arise in these unusual systems. To bring the excitement of practical theoretical nanoscience into undergraduate education, the PI plans to develop, improve, and enhance a new course entitled "Practicum on Computational Materials for Nanotechnology." This course will be offered to senior year students in Physics, Chemistry, Electrical Engineering, and Chemical Engineering. An outreach program aimed at attracting female high-school students to nanoscience will also be developed in collaboration with the Physics instructor at the LBJ Science Academy, a magnet high school with a large number of minority students. The PI aims to create an opportunity for female students to spend summers with the PI's research group to learn about computational nanoscience. This activity will be coordinated with a successful existing UTEACH program at UT.
The goal of this proposal was to develop a comprehensive theoretical framework for the emerging field of nanoscale epitaxial oxide semiconductor systems. These are novel hybrid nanostructures that combine properties of common semiconductors, such as silicon, with exotic functionalities such as ferromagnetism or ferroelectricity of transition metal oxides such as for example, BaTiO3. Such structures are expected to find applications as new sensors, smarter electronic components, and novel optoelectronic devices. The focus of the project was to identify through computer simulations key elements that enable the practical creation of these functional structures and thus aid the development of a new technology, and to explore new physical effects offered by these unusual systems. Keeping in mind technological applications of fundamental research was central to the spirit of this proposal. We have made significant contributions to the field of oxide/semiconductor epitaxy. The theoretical work, done under this project, enabled the PI to start the Materials Physics Laboratory, where many ideas developed through computer modeling are now being tested in practice (www.ph.utexas.edu/~aadg/lab/index.html). These include integration of ferromagnetic and ferroelectric materials on silicon for applications in the transistor technology. The first one may have application in spintronics, where in addition to charge the spin of electron is used. And the second one may result in very low power transistors that are needed for mobile computing. Another somewhat unexpected development is the integration of photocatalytic titanium dioxide on silicon with potential applications in water splitting by sunlight. The project supported studies of two doctoral students, two master students and one undergraduate student, who collectively published 37 research articles.
