Technical: In this Grant Opportunities for Academic Liaison with Industry (GOALI) project, the growth and collective electronic excitation properties of quasi-one-dimensional semiconductor materials are investigated. The vapor-phase growth of multi-component, uniform- and tapered-diameter nanowires of group III-V semiconducting materials uses the technique of metallorganic chemical vapor disposition. The structural, electronic, and optical properties of the nanowires are investigated using high-resolution electron microscopy, optical excitation spectroscopies, resonant Raman scattering, and proximal characterization methods. These studies are to elucidate how topological driven strain, surface and interface structure, and band structure, and band bending influence the presence and properties of collective electronic excitation within semiconductor heterostructure materials systems. The research projects are carried out collaboratively among students and faculty at Drexel University and industrial scientists at Structured Materials Industries, Inc. (SMI). The research goal of this project is to understand how multi-component group III-V based semiconductor nanowire materials can be grown and processed in a manner that they enable confinement and control of charge-density waves for the purpose of tunable, resonant terahertz detection and emission.
The project addresses basic research issues in a topical area of materials science with high technological relevance. The fabrication of semiconductor nanowires and study of their collective electronic excitations and their response to electromagnetic waves would lead to applications in advancing the state-of-the-art in the fast and sensitive detection of terahertz and charged-particle radiation. This GOALI project provides opportunities for graduate and undergraduate students to receive training and accrue experience over extended stays in an industrial setting in areas highly relevant to their research and career interests. The project will also include international collaboration with scientists in Italy.
In this NSF GOALI project a Drexel University-led team investigated how excited electrons generated under light illumination move within, and near and across interfaces of selected combinations of semiconductor materials in nanoscale form. The model system for this project involves co-axial cylindrical semiconductor nanostructures known as core-shell nanowires. The electronic properties of these materials and their interfaces were investigated using a variety of experimental probes and simulation methods. Significant differences in how light couples to these materials in comparison with thin film counterparts suggest a strong influence of nanoscale finite size. The extraordinarily fast speed with which optically-generated electrons move was seen to depend on the presence of the shell. Signatures of the peculiar, unexpectedly non-linear nature of current flow owing to relaxation of electrons with excess energy were observed and studied. The results of this research include a new family of patent-pending devices based on different ways of controling and using the transfer of highly energetic electrons from different parts of the nanowire. With the discovery of new principles of tuning this transfer the materials investigated and others like them now can be considered candidates for a new generation of devices. These devices may find use, for example, in the detection detect and use of light and its characteristics sensitively in new ways, with potential applications in advanced imaging in security, defense, and medicine and health, and in low-power electronics for information technology. PhD students supported on this project received training in nanomaterials growth, device design and fabrication, data collection and analysis, and disseminated results in peer-reviewed publications and presentations at international scientific and technical conferences. Several undergraduate students from Drexel and from other univesities and colleges participated as mentored undergraduate researchers. Regular interactions of the PI and his student group members with scientists and engineers at GOALI industry collaborator Structured Materials Industries, Inc. (SMI, Inc.) in NJ in the form of regular visits and long-term stays enabled practical knowledge and information transfer and collaboration in the growth of semiconductor materials, and in the fabrication and characterization of nanoscale devices. The project also enabled participants to interact with international collaborators in Italy and Israel through short-term mobility visits, and with collaborators at the University of Alabama, Lehigh University, and the US Naval Research Laboraory through advanced characterizations. These interactions and products added value and impact to the scientific results and to the education and training of the participants.
