Date: 31/01/2011

Researchers working on improving GaN based LED performance

Dow Corning is collaborating with IMEC to bring Gallium Nitride (GaN) epi-technology on silicon wafers to a manufacturing scale. GaN, which belongs group III nitrides, offers high breakdown voltages, high electron mobility and saturation velocity due to its band gap of 3.4 eV. GaN/AIGaN heterostructures switch faster with high efficiency in the frequency range of GHz + compared to silicon. GaN also is the right material for making opto-electronic semiconductors in visible short-wavelength and UV region.

GaN based LED devices are presently made depositing GaN film on sapphire, zinc oxide, silicon carbide (SiC), and silicon using Metal-Organic Chemical Vapour Deposition (MOCVD) process, but the wafer size is limited to 6 Inches. In this collaborative research by Dow Corning and IMEC they are aiming to deposit directly on 8 Inch silicon wafers, yielding in more LEDs in single process flow.

On the performance front, researchers from North Carolina State University have now developed a new technique that reduces defects in the gallium nitride (GaN) films used to create LEDs, making them more efficient. Researchers could able trap the defects into created voids
on the film.

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," says Dr. Salah Bedair, a professor of electrical and computer engineering at NC State and co-author, with NC State materials science professor Nadia El-Masry, of a paper describing the research. "So, for a given input of electrical power, the output of light can be increased by a factor of two - which is very big." This is particularly true for low electrical power input and for LEDs emitting in the ultraviolet range.

"Without voids, the GaN films have approximately 10[to the 10th power] defects per square centimeter," Bedair says. "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," was published online Jan. 17 by Applied Physics Letters.

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