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Building Semiconductor Nano Structures Using Miniature Pyramids

a nano pyramid - file photo by PSU
Innsbruck - Oct 15th, 2001
Electronic components, such as transistors on computer chips, are increasingly becoming smaller, while their performance capabilities are growing.

It is expected that the dimensions of such components will be in the nanometre range from as early as 2010. However, once the dimensions are in the realm of nanometres, the semiconductor properties are subject to the laws of quantum mechanics and are, for instance, dependent on the geometric dimensions of the components.

At the Institute for Semiconductor and Solid State Physics at the University of Linz, GŁnther Bauer's team has, with the support of the Austrian Science Fund, succeeded in producing and characterising such semiconductor nanostructures. The Linz physicists envisage that one of the first areas of application will be in laser technology.

A nanometre is roughly equivalent to one hundred-thousandth of the diameter of a human hair. In as little as approximately ten years' time, the electronic industry will be using semiconductor components which measure approximately 30 to 50 nanometres and which possess the necessary properties for the relevant application. The Linz team can produce such miniature structures in a controlled process and determine their properties.

"There are two production methods: with the 'top down' method, different semiconductor materials such as silicon and germanium are grown on top of one another, thus forming a type of sandwich structure which is subsequently processed by means of lithography and etching.

"The electrical, optical and magnetic properties of these structures depend not only on the chemical composition, but also on the thickness and distortion of the layers," explains Bauer.

"With the 'bottom up' method, small, pyramid-shaped islands, measuring approximately 10 nanometres in height, are produced through so-called self-organised growth."

Since a temperature of approximately 600 degrees is required for the precipitation of these islands, the starting materials are automatically mixed and the germanium concentration increases from the base of the pyramid towards the tip. However the ratio of ingredients in turn influences the quantum mechanical properties, so the control of this ratio is therefore important.

Tomography for nano-pyramids
In order to be able to determine the characteristics of these nano-components precisely, the Linz group, in cooperation with physicists in Grenoble, have developed a tomographic X-ray process which allows quasi-sections to be cut through the mini-pyramids at different heights and the chemical composition to be determined. "In the case of a pyramid measuring 10 nanometres in height, we can follow the course of the material concentration precisely on the nanometre scale," explains Bauer.

Thanks to this success, the possibility of an application for the middle infrared, e.g. in laser technology, becomes feasible. "The pyramids could be installed in resonators to create lasers which work with lower threshold currents than conventional lasers. This would certainly extend the service life of such components considerably," says Bauer.

Further research into the controlled growth and the structural, electronic and optical properties of such nano-components is certainly required over the coming years.

Related Links
Institute for Semiconductor and Solid State Physics - Linz
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Bucky Balls Get Superconductive
Murray Hill - Aug. 30, 2001
Scientists from Lucent Technologies' Bell Labs have shown that soccer ball-shaped carbon molecules known as bucky balls can act as superconductors at relatively warm temperatures, raising hopes for inexpensive, power loss-free organic electronics and other practical applications such as quantum computers.
Clues To Early History Of Solar System's Oldest Diamonds
Munich - August 09, 2001
Simulating implantation of noble gases into terrestrial diamond grains, scientists from the Karpov Institute for Physical Chemistry (Moscow, Russia) and the Max Planck Institute for Chemistry (Mainz, Germany) infer a sequence of events in the early life of diamonds in meteorites, the most common form of stardust available for laboratory study (Nature, August 9, 2001).
Earthquakes Reveal Diamonds' Origins
Tempe - July 13, 2001
The seismic rumblings could provide key clues about where miners should look for diamonds, according to recent research. Matt Fouch, assistant professor of geological sciences at ASU, studies vibrations caused by earthquakes to visualize the earth at depths of hundreds of kilometers, where diamonds are formed.
Superconductivity Taken To The Nanoth Degree
Hong Kong - July 9, 2001
Physicists at the Hong Kong University of Science and Technology have discovered that, below 15 K, single 4-Angstrom-carbon nanotubes exhibit superconductivity. This is the first time single-carbon nanotubes have been found to show superconducting properties, i.e., conducting electricity without resistance.

Molecular Rulers Enabling Precise Nanoscale Construction
University Park - Feb. 13 2001
Scientists at Penn State have discovered an effective and precise way to make ultraminiature metal wires in very close proximity to each other. Their work -- important because nanoscale construction methods have been limited to structures with larger, less controlled spacings -- is expected to be useful in the effort to further miniaturize electronic and opto-electronic devices used for circuits, high-density data storage, and sensors.

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