CAREER: Defects and Polarons in Complex Materials

University Of Delaware, Newark DE

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports research and education on the computational modelling of defects in complex materials that are used for energy, electronics, and optoelectronics applications. Defects play a crucial role in altering the properties of many materials, some of which are of high technological relevance and central to our daily life. For example, the electrical conductivity of semiconductors such as silicon and gallium arsenide can be drastically modified by adding minute concentrations of impurities, enabling a variety of microelectronic devices (such as the ubiquitous transistor) that are present in the microchips inside our current computers, smart phones, and tablets. On the other hand, defects can be detrimental to device performance, as is the case for defects that limit the efficiency of solar cells. Our ability to control the type and amount of defects present determines if a given material will be suitable for device applications. Understanding and controlling defects is therefore crucial to the development of novel materials for electronics and optoelectronics. Using advanced methods of electronic structure theory and supercomputers, the PI will investigate the role of defects in a series of complex materials that exhibit an array of exciting physical properties. The research may enhance the existing properties, and could lead to the discovery of new ones that can be used in novel device designs. In addition, this project will have significant educational value, incorporating training of graduate and K-12 high-school students. The graduate students will learn cutting-edge computational methods and advanced concepts in materials theory; they will also participate in an outreach program that involves teaching scientific programing to high-school students, enticing them to a career in science and technology. Through summer internships, high-school students will work on developing data-manipulation tools that will help the graduate students with complex data visualization. The tools will be freely available through the PI's research website. TECHNICAL SUMMARY This CAREER award supports research and education on the computational modelling of defects and charge localization in complex materials that are used for energy, electronics, and optoelectronics applications. The properties of most materials are strongly affected by the presence of defects. For example, adding minute concentrations of impurities to a semiconductor can drastically change its electrical conductivity by several orders of magnitude, transforming a good insulator into an excellent conductor. Defects can also be detrimental to device performance, as in the case of solar cells, where defects cause unwanted nonradiative carrier recombination, and strongly impact efficiency. Computer modelling based on density functional theory has turned into a powerful tool in the study of defects in various types of materials, providing information on concentrations, and on electrical and optical activities. These calculations often complement experiments by giving access to important properties and phenomena that are difficult to probe at the atomic scale. In this project the PI will use state-of-the-art computational methods to investigate the role of defects in oxides made of elements with partially filled d or f shells. The materials of interest include perovskites, layered perovskites, and pyrochlores. These materials have potential to enable novel devices and functionalities, as their most interesting properties are strongly influenced by the presence of impurities and defects. This project will advance fundamental understanding of the impact of defects and impurities on the electronic and optical properties of these complex materials. In a crucial step towards enabling device applications, the project will provide information on equilibrium defect concentrations, electrical and optical activities, and the relation between defects and charge carriers and migration. Ultimately, it will serve to identify defects that are detrimental to materials performance in devices, and will provide a basis to engineer defects, through doping or alloying, to enhance or broaden materials functionality. In addition, this project will have significant educational value, incorporating training of graduate and K-12 high-school students. The graduate students will learn cutting-edge computational methods and advanced concepts in materials theory; they will also participate in an outreach program that involves teaching scientific programing to high-school students, enticing them to a career in science and technology. Through summer internships, high-school students will work on developing data-manipulation tools that will help the graduate students with complex data visualization. The tools will be freely available through the PI's research website.