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Small structures bring big impact in electronics design

Posted: 30 Apr 2013     Print Version  Bookmark and Share

Keywords:semiconductor  nanowires  gallium arsenide  aluminium gallium arsenide 

A device that is 1,000 times thinner than the typical human hair may be the key to improved solar power harnessing, more effective air quality sensors and even stronger security measures against biological weapons (i.e. anthrax).

New research entitled "Optical, Structural and Numerical Investigations of GaAs/AlGaAs Core-Multishell Nanowire Quantum Well Tubes" and led by University of Cincinnati (UC) physics professors Howard Jackson and Leigh Smith reveal a new structure in a semiconductor nanowire with unique properties. "This kind of structure in the gallium arsenide/aluminium gallium arsenide system had not been achieved before," Jackson said. "It's new in terms of where you find the electrons and holes, and spatially it's a new structure."

These little structures could have a big effect on a variety of technologies. Semiconductors are at the centre of modern electronics. Computers, TVs and cell phones have them. They're made from the crystalline form of elements that have scientifically beneficial electrical conductivity properties.

Many semiconductors are made of silicon, but in this case they are made of gallium arsenide. And while widespread use of these thin nanowires in new devices might still be around the corner, the key to making that outcome a reality in the coming years is what's in the corner.

By using a thin shell called a quantum well tube and growing it—to about 4nm thick—around the nanowire core, the researchers found electrons within the nanowire were distributed in an unusual way in relation to the facets of the hexagonal tube. A close look at the corners of the tube's facets revealed something unexpected—a high concentration of ground state electrons and holes.

"Having the faceting really matters. It changes the ballgame," Jackson said. "Adjusting the quantum well tube width allows you to control the energy—which would have been expected—but in addition we have found that there's a highly localized ground state at the corners which then can give rise to true quantum nanowires."

The nanowires the team uses for its research are grown at the Australian National University in Canberra, Australia.

Nanowires hexagonal facets

These cross-sectional electron microscope images show a quantum well tube nanowire's hexagonal facets and crystal quality (left), and electron concentration in its corners.

The team's discovery opens a new door to further study of the fundamental physics of semiconductor nanowires. As for leading to advances in technology such as photovoltaic cells, Jackson said it is too soon to tell because quantum nanowires are just now being explored. But in a world where hundreds of dollars' worth of technology is packed into a 5-by-2.5 inch iPhone, it's not hard to see how small but powerful science comes at a premium.

The team at UC is one of only about a half dozen in the United States conducting competitive research in the field. It's a relatively young discipline, too, Jackson said, and one that's moving fast. For such innovative science, he noted it is important to have a collaborative effort.

The team includes scientists from research centres in Miami University of Ohio, Sandia National Laboratories in California, and Monash University and the Australian National University in Australia.

Jackson and Smith are joined by recently graduated PhD student Melodie Fickenscher and physics doctoral student Teng Shi and other scientists from their research partners.

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