THE NEXT BIG THING Making Silicon Nanowires.... Military Meta Materials Measuring Tiniest of Structures Shining a Light on Cancer Amazing Metal Nanoclusters Studying Nanostructured Materials Improving Key Cancer Weapon Nanoscale Optical Structures The Nanoelectronic Future Microelectronics Fabrication Teaching Old Process New Tricks Nanobelts Join World of Ultra-small

The Next Big Thing:
Teaching an Old Process New Tricks

In the microelectronics industry, molecular beam epitaxy (MBE) is used to grow thin films of materials with atomic-scale precision. April Brown and graduate student Jeng-Jung Shen are pushing the limits of MBE, hoping to gain more control of the process – enough to produce self-assembled quantum dots in the right sizes and locations for a new generation of electronics.

photo by Gary Meek Molecular beam epitaxy (MBE) has long been important to microelectronics research. April Brown is pushing the limits of MBE to produce self-assembled quantum dots that could have novel applications to future generations of electronic devices. (300-dpi JPEG version - 857k)

Self-assembled quantum dots. (Larger JPEG version - 54k)

Quantum dots are bundles of atoms, typically 100 atoms in diameter and 10 atoms high. Because their electrons are confined to such a small area, the tiny structures possess unique properties that may be useful in the next generation of electronic devices.

But before MBE can be used to grow quantum dots useful to nanoelectronics, researchers must learn to control MBE well enough to consistently produce structures with uniform sizes in desired locations. Current technology produces randomly spaced quantum dots that often grow too large.

"We'd like to be able to absolutely control where they are deposited, where they nucleate and what their size is," explains Brown, a professor in the School of Electrical and Computer Engineering. "The perfect material would be a three-dimensional volume in which you have an array of uniformly sized, regularly spaced quantum dots."

Brown's research team already grows three-dimensional arrays in which successive layers of quantum dots grow atop one another, separated by thin semiconductor films. The dots grow because of a cleverly mismatched crystalline structure; self assembly occurs because mechanical stresses in the successive layers encourage quantum dot growth at distortions in the crystalline structure. It's an impressive feat, but the researchers still cannot control where the first layer of dots forms.

"It's going to be difficult to achieve," Brown admits. "It's going to have to be achieved with surface patterning or some other technique yet to be developed."

The issue has relevance to more than quantum dots. If researchers can reach this goal, what they will learn will help them improve more conventional MBE applications – including Brown's long-term work with heterojunction devices formed at interfaces between dissimilar materials.

The work is supported by the Office of Naval Research, the Defense Advanced Research Projects Agency and the Air Force Research Laboratory.

For more information, contact April Brown, School of Electrical and Computer Engineering, Georgia Tech, Atlanta, GA 30332-0269. (Telephone: 404-894-5161) (E-mail: april.brown@ece.gatech.edu)