Doubling Up LED Output

February 1, 2011 | 2 Comments

Dr. Salah Bedair, a professor of electrical and computer engineering at North Carolina State University and co-author materials science professor Nadia El-Masry have developed a new LED building technique that reduces defects in the gallium nitride (GaN) films used to create LEDs, making them more efficient.

Bedair explains, LED lighting relies on GaN thin films to create the diode structure that produces light. The new technique reduces the number of defects in those films by two to three orders of magnitude. “This improves the quality of the material that emits light. So, for a given input of electrical power, the output of light can be increased by a factor of two – which is very big,” he said.  This is particularly true for low electrical power input and for LEDs emitting in the ultraviolet range.

LED Diagram.

LEDs are an increasingly popular technology for use in energy-efficient lighting and should overtake the compact florescent lamps with continued price reductions.  A doubling of the output per unit or per power consumption has to help in production costs, driving to lower prices.

The NCSU team research focused on the common GaN thin films used to create the diode structure that produces light beginning with a GaN film that was two microns, or two millionths of a meter, thick and embedded half of that thickness with large voids – empty spaces that were one to two microns long and 0.25 microns in diameter. The researchers found that defects in the film were drawn to the voids and became trapped – leaving the portions of the film above the voids with far fewer defects.

Defects are slight dislocations in the crystalline structure of the GaN films. These dislocations run through the material until they reach the surface. By placing voids in the film, the researchers effectively placed a “surface” in the middle of the material, preventing the defects from traveling through the rest of the film.

The voids make an impressive difference.

Bedair says, “Without voids, the GaN films have approximately 10[to the 10th power] defects per square centimeter. With the voids, they have 10[to the 7th power] defects. This technique would add an extra step to the manufacturing process for LEDs, but it would result in higher quality, more efficient LEDs.”

The paper, “Embedded Voids Approach for Low Defect Density in Epitaxial GaN Films,” published online Jan. 17 by Applied Physics Letters describes developing defect reductions in GaN epitaxial films grown on sapphire substrates. This technique relies on the generation of high densities of embedded microvoids (~108/cm2), a few microns long and less than a micron in diameter. These voids are located near the sapphire substrate, where high densities of dislocations are present. The network of embedded voids offer free surfaces that act as dislocation sinks or termination sites for the dislocations generated at the GaN/sapphire interface.

The paper was co-authored by Bedair and El-Masry with Pavel Frajtag, a Ph.D. student at NC State and Dr. N. Nepal, a former post-doctoral researcher at NC State now working at the Naval Research Laboratory. The research was funded by the U.S. Army Research Office.

This research looks to pay off handsomely for commercial makers looking to produce high value LED products.  Cutting the power consumption in half is remarkable, and a review hints that even more improvement is possible if not probable.  One has to wonder just how well an LED with no or near no defects might perform.

This writer finds the LED light output preferable to florescent and eagerly looks forward to more and better LED products.  Lets hope all manufacturers notice this work and the team stays at the effort to improve the LED.


2 Comments so far

  1. Matt Musson on February 1, 2011 10:51 AM

    Being able to use half the number of LED’s should significantly reduce the cost of the end product. LEDs are the future. CFL’s are just a stop gap.

  2. Ditto on February 6, 2011 10:19 PM

    Yes, I think so, too. But I’d be so happy if you give more detailed information. I want to make one on my own.

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