Home > Press > Researchers Peer Into Nanowires to Measure Dopant Properties
Abstract:
Semiconductor nanowires -- tiny wires with a diameter as small as a few billionths of a meter -- hold promise for devices of the future, both in technology like light-emitting diodes and in new versions of transistors and circuits for the next generation of electronics. But in order to utilize the novel properties of nanowires, their composition must be precisely controlled, and researchers must better understand just exactly how the composition is determined by the synthesis conditions.
Researchers Peer Into Nanowires to Measure Dopant Properties
Evanston, IL | Posted on April 2nd, 2009
Nanowires are synthesized from elements that form bulk semiconductors, whose electrical properties are in turn controlled by adding minute amounts of impurities called dopants. The amount of dopant determines the conductivity of the nanowire.
But because nanowires are so small -- with diameters ranging from 3 to 100 nanometers -- researchers have never been able to see just exactly how much of the dopant gets into the nanowire during synthesis. Now, using a technique called atom probe tomography, Lincoln Lauhon, assistant professor of materials science and engineering at Northwestern University's McCormick School of Engineering and Applied Science, has provided an atomic-level view of the composition of a nanowire. By precisely measuring the amount of dopant in a nanowire, researchers can finally understand the synthesis process on a quantitative level and better predict the electronic properties of nanowire devices.
The results were published online March 29 in the journal Nature Nanotechnology.
"We simply mapped where all the atoms were in a single nanowire, and from the map we determined where the dopant atoms were," said Lauhon. "The more dopant atoms you have, the higher the conductivity."
Previously, researchers could not measure the amount of dopant and had to judge the success of the synthesis based on indirect measurements of the conductivity of nanowire devices. That meant that variations in device performance were not readily explained.
"If we can understand the origin of the electrical properties of nanowires, and if we can rationally control the conductivity, then we can specify how a nanowire will perform in any type of device," said Lauhon. "This fundamental scientific understanding establishes a basis for engineering."
He and his group performed the research at Northwestern's Center for Atom Probe Tomography, which uses a Local Electrode Atom Probe microscope to dissect single nanowires and identify their constituents. This instrumentation software allows 3-D images of the nanowire to be generated, so Lauhon could see from all angles just how the dopant atoms were distributed within the nanowire.
In addition to measuring the dopant in the nanowire, Lauhon's colleague, Peter Voorhees, Frank C. Engelhart Professor of Materials Science and Engineering at Northwestern, created a model that relates the nanowire doping level to the conditions during the nanowire synthesis. The researchers performed the experiment using germanium wires and phosphorous dopants -- and they will soon publish results using silicon -- but the model provides guidance for nanowires made from other elements, as well.
"This model uses insight from Lincoln's experiment to show what might happen in other systems," Voorhees says. "If nanowires are going to be used in device applications, this model will provide guidance as to the conditions that will enable us to add these elements and control the doping
concentrations."
Both professors will continue working on this research to broaden the model.
"We would like to establish the general principles for doping semiconductor nanowires," said Lauhon.
The paper is titled "Direct Measurement of Dopant Distribution in an Individual Vapour-liquid-solid Nanowire." In addition to Lauhon and Voorhees, the other authors are Daniel E. Perea, Eric R. Hemesath, Edwin J. Schwalbach and Jessica L. Lensch-Falk, all from Northwestern.
The Office of Naval Research and the National Science Foundation supported the research.
####
About Northwestern University
Research thrives at Northwestern University, with an annual budget of over $1.5 billion and more than $439 million in sponsored research. At Northwestern, and often with partners at Argonne National Laboratory, Fermilab, and local universities, interdisciplinary teams work to solve society's problems and facilitate clinical and commercial use of their innovations.
For more information, please click here
Contacts:
Megan Fellman
(847) 491-3115
Copyright © Northwestern University
If you have a comment, please
Contact us.
Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Bookmark:
Northwestern’s Center for Atom Probe Tomography
News and information
How do cold ions slide May 24th, 2013
Heinrich Rohrer dies at 79; a father of nanotechnology: With IBM colleague Gerd Binnig, Rohrer invented the scanning tunneling microscope, which can show individual atoms on a surface and move them around May 23rd, 2013
Gold nanocrystal vibration captured on billion-frames-per-second film May 23rd, 2013
Glowing Plant Releases Maker Kit, Enabling Anyone to Make a Glowing Plant at Home: Glowing Plant seeks funds via crowdfunding and raises almost $400,000 May 23rd, 2013
Possible Futures
Lifeboat publishes its first book: The Lifeboat Foundation has published its first book, "The Human Race to the Future: What Could Happen -- and What to Do" May 14th, 2013
UC Santa Barbara History Professor's Book Elucidates, Celebrates ‘Visioneers' May 14th, 2013
Conceptual Nanomedical Lipofuscin Removal Strategy April 29th, 2013
The Global Desalination Market 2013-2023 April 24th, 2013
Nanoelectronics
Imec and Renesas collaborate on ultra-low power short range radios: Collaboration will develop robust wireless solutions for future electronics May 16th, 2013
Piezoelectric 'taxel' arrays convert motion to electronic signals for tactile imaging April 25th, 2013
Battery and Memory Device in One April 25th, 2013
Secret of the Crystal's Corners: New Nanowire Structure Has Potential to Increase Semiconductor Applications: University of Cincinnati research describes discovery of a new structure that is a fundamental game changer in the physics of semiconductor nanowires April 23rd, 2013
Announcements
How do cold ions slide May 24th, 2013
Heinrich Rohrer dies at 79; a father of nanotechnology: With IBM colleague Gerd Binnig, Rohrer invented the scanning tunneling microscope, which can show individual atoms on a surface and move them around May 23rd, 2013
Gold nanocrystal vibration captured on billion-frames-per-second film May 23rd, 2013
Glowing Plant Releases Maker Kit, Enabling Anyone to Make a Glowing Plant at Home: Glowing Plant seeks funds via crowdfunding and raises almost $400,000 May 23rd, 2013