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Mar 4th, 2013
Brighter, smarter and more efficient LEDs thanks to nanoscale roughening of the LED surface
Ming Ma, a doctoral student in the Department of Materials Science and Engineering at Rensselaer Polytechnic Institute, has developed a new method to manufacture light-emitting diodes (LEDs) that are brighter, more energy efficient, and have superior technical properties than those on the market.
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  • Graded-refractive-index (GRIN) structures help to improve the light-extraction efficiency
  • A light-extraction efficiency of 70 percent has been demonstrated

His innovation holds the promise of hastening the widespread adoption of LEDs and reducing the overall cost, energy consumption, and environmental impact of illuminating our homes and businesses.

Ma’s project is titled “Graded-refractive-index (GRIN) Structures for Brighter and Smarter Light-Emitting Diodes.
Over the past decade, there has been a profound shift in the way we light our homes, offices, and businesses. Conventional incandescent and fluorescent light sources are increasingly being replaced by more energy-efficient, longer-lived, and environmentally friendlier LEDs. Beyond illumination, researchers and companies are finding new uses for LEDs in areas as diverse as communication, health care, and imaging.

Improving the efficiency of LEDs and introducing new functionalities such as controllable light emission patterns are critical steps to continuing and accelerating their widespread adoption. One major challenge still needing to be solved is improving the low light-extraction efficiency of LEDs—or the percentage of produced light that actually escapes from the LED chip. Currently, most unprocessed LEDs have a light-extraction efficiency of only 25 percent, which means 75 percent of light produced gets trapped within the device itself.

One solution that has emerged is to roughen the surface of LEDs, in order to create nanoscale gaps and valleys that enable more light to escape. While surface roughening leads to brighter and more efficient light emission, the roughening process creates random features on the LED’s surface that do not allow for a complete control over other critical device properties such as surface structure and refractive index.

Ma’s solution to this problem was to create an LED with well-structured features on the surface to minimize the amount of light that gets reflected back into the device, and thus boost the amount of light emitted. He invented a process for creating LEDs with many tiny star-shaped pillars on the surface. Each pillar is made up of five nanolayers specifically engineered to help “carry” the light out of the LED material and into the surrounding air.

Ma’s patent-pending technology, called GRIN (graded-refractive-index) LEDs, has demonstrated a light-extraction efficiency of 70 percent, meaning 70 percent of light escaped and only 30 percent was left trapped inside the device—a huge improvement over the 25 percent light-extraction efficiency of most of unprocessed LEDs. In addition, GRIN LEDs also have controllable emission patterns, and enable a more uniform illumination than LEDs.

Overall, Ma’s innovation could lead to entirely new methods for manufacturing LEDs with increased light output, greater efficiency, and more controllable properties than both surface-roughened LEDs and the LEDs currently available in the marketplace.



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