Growth of Tensile Germanium Nanowires Embedded in a III-V Matrix

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Non-technical Description: Many of the properties of electronic and photonic materials are determined by the length of and the angle between their chemical bonds. Stress and strain can slightly alter these bonds, but cause profound changes in the way that materials interact with both light and electrical charge. Germanium is particularly noteworthy in this regard. A 2% change in bond length enables it to emit light very efficiently while in its normal state, germanium is a poor light emitter. This project seeks to engineer the properties of germanium nanostructures by embedding them into a matrix that induces stress. Nanocomposites formed from Ge nanostructures embedded in a foreign host enable new optical and electrical properties. The research project is integrated with the education and outreach activities. Besides interdisciplinary research training provided at the graduate and undergraduate levels, the PI schedules regular meetings with junior faculty in engineering to discuss how K-12 outreach can improve work-life balance, a growing concern among academic scientists. Through these outreach activities, he uses his personal experience to encourage junior faculty members in developing innovative outreach activities. Another activity involves pre-college outreach to talented seniors at Wilbur Cross High School, a racially and economically diverse public high school in New Haven. Technical Description: This project aims to demonstrate novel nanocomposite materials consisting of tensile-strained Ge nanowires embedded in III-V matrices. Recent research has shown that the properties of Ge nanomembranes, nanowires, microdisks, and microbridges can be tuned using external stressors to apply large biaxial or uniaxial tensile strains. In this project, surface-mediated phase separation during molecular beam epitaxy growth is investigated as a new approach to grow epitaxial Ge nanostructures embedded in a III-V matrix with high tensile strain. Specifically, Task 1 seeks to draw connections between growth conditions, structure, and properties of Ge/III-V nanocomposites, including basic understanding of interfacial strain coupling; Task 2 focuses on the coupled effects of matrix composition and lattice constant on the kinetics of Ge phase separation and the resulting microstructures. Finally task 3 seeks to understand the changes in structure and properties when the nanowires are modulated into nanorods or quantum dots. The ability to design and grow Ge/III-V nanocomposites with previously unattainable strain states may lead to a range of unprecedented material properties for Ge, such as the indirect-gap to direct-gap conversion or even becoming a semi-metallic material. Moreover, the fundamental understanding of epitaxial nanocomposites could apply to a wide range of other material systems such as complex oxides, dilute magnetic semiconductors, and highly mismatched alloys.