GaN depo process said to make brighter LEDs
R Colin Johnson
1/25/2011 9:47 PM EST
PORTLAND, Ore.—A new gallium nitride (GaN) process purifies that high-energy material by eliminating up to 1,000 times as many defects as are typically present, according to its inventors at North Carolina State University (NCSU).
The NCSU researchers predict that light-emitting diodes (LEDs), power transistors and other devices cast in GaN will be able to double their outputs by switching to the new process.
The process, invented by EE professor Salah Bedair and materials-science professor Nadia El-Masry, intentionally introduces voids into the GaN film near its interface with a sapphire substrate. As a result, the thousands of defects typically present are sucked into the voids thereby boosting the output of the devices using that purified film.
"The voids act like sinks for defects and dislocations near the interface, as well as acting as expansion joints for lattice mismatches," said Bedair. "We are in the process of measuring its affect on devices. Besides LEDs, we also believe that other GaN devices, like power transistors, could experience improved performance and reliability by using our process."
Bedair discovered the technique accidentally when his graduate student, Pavel Frajtag, complained that nanowires had formed in its bulk-grown GaN films when using a maskless inductively coupled plasma-reactive ion etching technique. Bedair asked him to get rid of the nanowires using epitaxial overgrowth, which resulting in the void formation and dislocation trapping effect that purified the film by 1,000X.
The GaN film tested was about two microns thick with ellipsoid shaped voids of about 0.25 micron in diameter surrounded by a film with 1,000-times fewer defects. The voids themselves did not degrade the performance of the film, but on the contrary were estimated by the researchers estimate to double its output.
Currently the researchers are characterizing the material further, as well as building LEDs and other devices with the process in order to prove its ability to boost GaN device's outputs.
A new process for gallium nitride (GaN) films removes efficiency robbing defects--dark streaks (a)--by trapping them in voids--elipsoids (b).