Technical Description: Non-planar heterostructures, particularly core-shell nanowires, exhibit a number of comparative advantages for optoelectronic applications with respect to conventional planar heterostructures. The analysis of dopant distribution and interface morphology is extremely challenging, however, limiting the understanding of fundamental growth processes that is needed to optimize the structure and properties. This project investigates the driving forces that control dopant and alloy element incorporation, diffusion, and segregation in non-planar heterostructures consisting of both Si-Ge and GaAs-AlGaAs core-shell nanowires. To this end, atom probe tomography, Hall effect measurements, Kelvin probe force microscopy, and micro-photoluminescence are used to relate doping levels, and fluctuations in composition, to electronic and optical properties. Numerical modeling of dopant diffusion during processing and electrical transport in device structures is based on and compared with quantitative, atomic scale composition information provided by the atom probe studies.
Non-technical Description: New materials, and conventional materials in new forms, can improve existing technologies and lead to the creation of new technologies. This project is developing a fundamental understanding of how known semiconductor materials, such as silicon and gallium arsenide, can be put together in new ways to better perform important functions, such as the efficient conversion of light to electrical energy and vice versa. The research activity is specifically focused on non-planar heterostructures, where "heterostructure" indicates the combination of two distinct materials and "non-planar" indicates that the junction between these materials has a complex three-dimensional form so as to better carry out key device functions. To analyze the shape of non-planar heterostructures and the distribution of tiny quantities of charge-controlling dopant atoms within them, a highly specialized microscope known as an atom probe tomographic is employed. The atom probe can look inside the very smallest devices that have ever been made and map out the distribution of all the elements that are present. The project incorporates an industrial perspective on the development of materials for new technologies by including a "co-op on campus" program, in which undergraduate research projects of relevance to the larger goals of the research are solicited from industrial partners.
