l to examine dots, realized they had another.
Floro, along with Bob Hwang (a California-based Sandia researcher), Ray Twesten at the University of Illinois at Urbana-Champaign, Eric Chason (a former Sandia researcher) and Ben Freund of Brown University, made measurements that treat dots as the originators of light-interference patterns. Since light's direction and intensity varies depending on the size, shape, and spacing of the islands, the results offer information in real time to determine what is happening to the tiny islands as temperatures, material compositions, and stresses change.
"We realized that if we could produce islands more than 1,000 angstroms across, the spacing between islands was like that of a diffraction grating," says Floro. "Combined with our real-time stress observations, this allowed us to measure stress, shape, and size simultaneously instead of having to stop the process, take the dots out, and measure them. A key ingredient was our ability to show that the basic physics of the large islands mimics that of the much smaller dots."
Observing the process of dots going from one shape to another to relieve stress provided deep insight into the physics governing island formation. "It showed us what controls dot evolution, and how process conditions like temperature and strain enhance or suppress dots."
Silicon germanium is not a good laser emitter, but it is simple enough to derive the applicable physics. "We next need to find out next how much of the physics learned in silicon germanium will apply to real laser materials like indium gallium arsenide," says Floro. "If we can understand the physics, we can make better quantum dots."
The DOE Office of Basic Energy Sciences, Division of Materials Sciences, funds the work.
Cite This Page: