While one proven way to increase the light extraction efficiency of LEDs is to
roughen the surface, the random features on the LED’s surface can challenge the process of light control in the absence of a secondary optic. Ming Ma, a doctoral student Department of Materials Science and Engineering at
Rensselaer Polytechnic Institute, has devised method that enables 70 percent
light extraction that controls the surface structure and refractive index Ma is
one of three finalists for the 2013 $30,000 Lemelson-Rensselaer Student Prize
for his project titled, “Graded-refractive-index (GRIN) Structures for
Brighter and Smarter Light-Emitting Diodes.” Ma invented a process for
creating LEDs with many tiny star-shaped pillars on the surface. Each pillar is
made up of five nanolayers engineered to help “carry” the light out
of the LED material and into the surrounding air.
The star-shaped pillars on the surface help to minimize the amount of light
that gets reflected back into the device, and thus boost the amount of light
emitted. 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.
The details were published in the October issue of Applied Physics Letters.
Phys. Lett. 101, 141105 (2012))