New technology promises brighter, longer-lasting LEDs

May 22, 2003

Sandia researcher Christine Mitchell looks through a substrate that was made for the new cantilever-epitaxy growth process.

Researchers at Sandia National Laboratories developed a new way to help light up the world with brighter green, blue, and white semiconductor LEDs. The process, called cantilever epitaxy, involves growing gallium nitride on an etched sapphire substrate. Conventionally, LEDs have been grown with various combinations of gallium-nitride alloys on sapphire substrates. However, the atoms of the two materials don't line up perfectly due to bond length differences in their respective crystal lattices. Regions of imperfections, or dislocations, accommodate the lattice mismatch, limiting LED brightness and performance.

Using the cantilever-epitaxy process, Sandia researchers reduce the number of dislocations for longer lasting and better performing LEDs. Using scanning electron microscopy (SEM) and similar techniques, researchers determined the amount of dislocations eliminated through the cantilever-epitaxy process. The images showed that facets developed early in the cantilever growth process can turn dislocations effectively when they are grown to full pyramids.

Sandia researcher Carol Ashby says that the reduction in dislocations means the cantilever-epitaxy process shows "great promise for making a superior substrate for light-emitting devices." Cantilever epitaxy of gallium nitride is being considered for high-electron-mobility transistors in miniature synthetic aperture radar systems (SAR) and high-efficiency solid-state lighting.

Gallium nitride can also be made to emit ultraviolet light, and compact solid-state UV emitters would be useful in detecting biological and chemical toxins for homeland security applications.

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