RALEIGH -- An experiment in Salah Bedair's lab at N.C. State University generated curious holes in gallium nitride, a semiconductor material used to make light-emitting diodes.
LEDs are microscopically small, square slivers that produce light when electricity runs through them. Each square consists of row upon row of crystals lining up like stitches in a knitting pattern.
One of Bedair's students and a postdoctoral fellow were trying out a spiky scaffolding of nanowires to grow the crystal layers. Nobody expected the nanowires would create holes in the bottom half of the LED.
"Once I saw the voids I knew what they would do," Bedair said. He just needed proof.
Bedair, a professor of electrical and computer engineering on NCSU's Centennial Campus, suspected the holes would reduce the number of defects in the crystalline knitting pattern and make the LED more efficient. Tests showed he was right, which could be a big deal.
LEDs already convert four to five times more electric energy into light than incandescent light bulbs.
So far, LEDs have been used in appliances, electronics and lights for traffic signals, parking lots and buildings. They are also starting to appear in residential lighting.
Widespread adoption of LEDs could reduce greenhouse gas emissions and save an estimated $120 billion in energy costs over 20 years, the U.S. Department of Energy estimates. But LEDs first have to become cheaper and more efficient.
Defects in gallium nitride production are like wrong stitches that carry from the bottom to the top row of a knitting pattern, Bedair said. Halfway up the pattern, the defects run through a layer of gallium nitride and indium nitride. This layer is where the electricity generates the light that makes an LED shine, and the defects force the electricity to make detours.
The holes catch the defects just below the indium gallium nitride layer and stop them from running through it, lab tests showed. As a result, electricity is less impeded as it flows through the indium gallium nitride layer, and the LED shines brighter.
"For a given input of electrical power, the output of light can be increased by a factor of two, which is very big," Bedair said.
