Machine Design

Green light for white LEDs

A team of Polytechnic Institute researchers aims to close the gap" in LED technology by doubling or tripling power output of LEDs in three years, an advance that could lead to the replacement of incandescent and fluorescent lamps.

Brighter green LEDs could help render incandescent bulbs obsolete.

The work follows the DoE solid-state lighting accelerated roadmap, which calls for development by 2025 of solid-state lighting technologies that are much more energy efficient, longer lasting, and cost competitive than conventional lighting.

The prime contender to meet this goal is a white-light unit made from a combination of high-performance red, blue, and green LEDs. Researchers have advanced the design of red and blue LEDs, but the technology behind green LEDs has lagged substantially, says the group. Green light is an essential piece of the puzzle because it addresses the peak of humanvision sensitivity, providing balance to the red and blue light.

The conventional process for making green LEDs adds indium (In) to gallium nitride (GaN), the material from which blue LEDs are fabbed. Such green LEDs are inefficient and too dim for lighting homes and offices. The indium segregates under certain conditions, clustering in areas where there are already defects in the material, researchers explain. A correlation between indium clustering and limited performance has been proposed, but may just be a coincidence.

The group plans to instead focus on piezoelectric effects. Controlling it could lead to a process able to make higherintensity green LEDs that more efficiently convert electricity into light. The team has partnered with GaN substrate fab Kyma Technologies Inc., Raleigh, N.C., and Crystal IS Inc., Green Island, N.Y., a maker of single-crystal, aluminum-nitride (AlN) substrates used in blue and ultraviolet lasers. The research was one of 16 projects selected for funding through DOE's Solid-State Lighting Core Technologies Funding Opportunity Announcement. The initiative supports fundamental research in solid-state lighting technology for general illumination.

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