Event

MSE Seminar - Prof. Lincoln J. Lauhon, Northwestern University

Friday, May 9, 2008
1:00 p.m.
Rm. 2108, Chemical and Nuclear Engineering Bldg.
Annette Mateus
301 405 5207

"Deconstructing Semiconductor Nanowires: Atom-by-Atom Mapping of Dopants, Impurities, and Heterojunctions"

Semiconductor nanowires of controlled composition and doping show great promise as multifunctional components in emerging device technologies and provide new opportunities to explore the physics of electrons in reduced dimensions. The continued advancement of nanowire-based devices will depend critically on knowledge of their atomic-scale structure, as compositional fluctuations as small as a single dopant atom can affect device performance. Recently, we have made significant advances in quantitative nanoscale characterization that can provide a rational basis for engineering new or improved technologies based on semiconductor nanowire. Specifically, we have used atom probe tomography (APT) to map the distribution of dopant atoms in individual vapor-liquid-solid grown Si and Ge nanowires. We find that the doping efficiency is, in general, lower than expected, and that the dopant distribution is radially non-uniform, which has important implications for device performance and modeling. We have also used APT in conjunction with scanning transmission electron microscopy to investigate the incorporation of metal catalyst atoms in VLS-grown nanowires. Single Au atoms have been detected for the first time at levels above the equilibrium solubility. Diameter-dependent measurements of minority carrier diffusion lengths establish, however, that the nanowire surface controls the minority carrier lifetime. The application of scanning photocurrent microscopy to the analysis of majority and minority carrier transport characteristics in nanowire devices will also be discussed. By integrating the activities of nanowire synthesis, composition characterization, and quantitative nanoscale property measurement, we aim to determine the extent to which the properties of semiconducting nanowires can be rationally controlled by doping and composition modulation on the nanoscale.

For more information, contact Annette Mateus at (301) 405-5207 or amateus@umd.edu.