TROY, N.Y. — Rensselaer has received a $1.8 million, three-year grant from the U.S. Department of Energy (DOE) to develop green and deep green LEDs that are both more powerful and more efficient than current technology. These LEDs will be a major step toward DOE’s goal of replacing current lighting technology with efficient white LEDs by the year 2025, according to Christian Wetzel, associate professor of physics and a principal investigator on the grant.

Wetzel, a recognized leader in green LED technology, explained that in one of the most promising approaches to white LEDs, red, blue, and green LEDS must be combined in the right proportions. While there have been major advances in red and blue LEDs, green has proved more challenging. Although his research group already holds records for green LED performance, “we still have a long way to go,” he said.

Wetzel and co-principal investigator E. Fred Shubert are chaired members of Rensselaer’s Future Chips Constellation, which is known for its groundbreaking research in issues of lighting quality, power, and efficiency. The Constellation also includes physics professor Shawn Yu Lin. The grant will help support a post-doc researcher and four graduate students as well as the cost of many of the laboratory processes involved in the research, Wetzel said. He hopes to expand this lighting research group with additional grants.

The grant is one of 16 in this round of funding awarded by DOE to universities, national laboratories, and industrial research labs for fundamental research needed to advance the adoption of solid-state lighting technology. DOE’s goal is to reduce energy consumed by electric lighting by 50 percent by 2025, largely through a switch to solid-state lighting technology.

A number of challenges

Wetzel takes an integrated approach toward filling the “green gap.” In this project, he addresses a number of challenges.

Current solid-state materials used for green LEDs have high dislocation densities – the presence of many irregularities in their structure. Wetzel’s group will obtain bulk gallium nitride and aluminum nitride substrates with low dislocation densities from the subcontractors: Crystal IS, a firm that recently moved from the Rensselaer Incubator to the Tech Park, and Kyma Technologies of North Carolina. Conforming epitaxial growth procedures will be developed to maintain the substrate’s low dislocation density throughout the active region.

The project will “pay tribute to the piezoelectric aspect of the materials,” – their tendency to build-up electric charge under strain. Wetzel is recognized for demonstrating the importance of this trait on the band structure and the light emission process. Piezoelectric polarization will be controlled throughout the device structure by choosing bulk substrates with different crystallographic orientations.

Costs will be cut by developing methods to use vapor phase bulk growth, a less expensive form of processing, for thick layers instead of metalorganic vapor phase epitaxy.

In addition, Wetzel said, performance yield spectroscopy will support epitaxial growth optimization. He has developed band structure spectroscopy techniques to study the physics of light emission by materials. Now, he said, he will use that knowledge to help optimize materials.

Originally published May 2006 in the Rensselaer Research Update.

Published June 22, 2006