Doping Profiles in Semiconductor Nanowires

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Technical: Semiconductor nanowires are potentially transformative materials for electronics and photonics technologies, and doping and composition modulation are the foundation of semiconductor devices. The objective of this project is to understand and control dopant incorporation rates and junction profiles in silicon and germanium nanowires in order to establish a foundation for nanowire device fabrication. Atom probe tomography is used to map the 3-dimensional distribution of donor and acceptor dopant atoms in vapor-liquid-solid and vapor-solid-solid grown nanowires with single dopant atom sensitivity. Varied catalysts and growth conditions will be employed to understand the thermodynamic and kinetic factors that influence doping rates. Such understanding is expected to establish the ultimate limits of junction abruptness for both radial junctions, as in core-shell structures, and axial junctions. Electrical transport and scanning probe measurements, including scanning Kelvin probe microscopy and scanning photocurrent microscopy, are used to determine the fraction of active dopants and measure the electrical profiles of dopant homojunctions. The integrated activities of synthesis, composition mapping, and electrical characterization permit distinctions between electrical properties that arise from nanoscale dopant distributions and those that arise from modified screening on the nano/meso scale. Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. The activity is expected to advance materials and metrology of critical importance to the semiconductor industry. The project integrates research and education by advancing discovery and understanding through involvement of the PI and his graduate students in a new Student Investigative Research program at a local high school and engaging student groups from a senior level process design course in the discovery and optimization of nanowire processing-structure relationships.