Collaborative Research: Identifying and Controlling Conductivity Variations in Semiconductor Nanowires

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1604931 / 1603904 PIs: Shan, Jerry W. / Filler, Michael A. Title: Collaborative Research: Identifying and Controlling Conductivity Variations in Semiconductor NanowiresSemiconductor nanowires are emerging as important nanoscale building blocks for applications as diverse as energy harvesting, solid-state lighting, heat transfer, information processing, chemical detection, and even bioelectronics. These nanoscale materials exhibit significant variations in their structure and composition that can limit their function and properties. A better understanding and control of run-to-run variations in semiconductor nanowire synthesis will enable precise tuning of nanowire properties to yield ensembles with conductivity distributions far narrower than the current state-of-the-art. This project focuses on statistically assessing variations in the electrical conductivity of semiconductor nanowires, understanding the underlying causes for the variations, and developing methodologies that minimize the, in order to enable commercial applications. The research project involves coupling novel high-throughput electro-orientation spectroscopy (EOS) with state-of-the-art nanowire synthesis techniques. EOS is based on the frequency-dependent alignment rates of liquid-suspended nanowires subjected to an AC electric field and can measure the conductivity of about one thousand nanowires per day, hundreds of times faster than existing direct-contact approaches. A fundamental chemical understanding of nanowire growth allows for careful control of the hetero-interfacial processes that influence dopant incorporation. Preliminary data confirm that nanowire conductivity can vary considerably within an ensemble. The proposed work will focus on identifying the critical process parameters that affect electrical conductivity in semiconductor nanowires and on the development of new processes that reduce conductivity variations. Two classes of nanowires will be studied: (1) uniformly-doped Si and Ge nanowires of varying n and p character and (2) SiGe alloy, core-shell, and other heterogeneous nanowires. While Si and Ge nanowires are the focus of this project, the approach is expected to be applicable to a broad spectrum of other materials (e.g., III-V semiconductors, oxides, etc.). The project will involve cross-disciplinary and cross-university training of graduate students, recruiting of minority undergraduate students into pursuing research projects in the laboratories of the principal investigators, curriculum development activities, and an outreach effort aiming at engaging K-12 students into pursuing STEM careers.