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).
Can you point to a journal or conference publication or website with more information? Starting with what "EVA" stands for - Ellipsoidal Void A????
The pictured material is probably useful for solar cells or LEDs. I can't imagine patterning repeatable transistors or circuitry if the voids were not aligned with the pattern. OTOH, perhaps they can be seeded from an etched or implanted pattern. Worth learning more about!
Keith Lofstrom, Beaverton Oregon
This is primarily a materials advance, but the applications are numerous and growing. LEDs are the most abundant application of GaN today, but the binary III/V material is being used to take on all sorts of high-power and high-frequency applications that the this new process could potentially improve, from the laser diodes used in Blu-Ray disks to the high-power MOSFETs used in electric cars to future spintronic devices.
I think this is truly a breakthrough of huge implications potentially. GaN materials quality is either challenging or terribly expensive.
Sapphire is a reasonable MOCVD substrate cost compromise, but with typically crappy films. The method described is an extension of variants of nanowire growth regimes, - the modestly well known wire to wine-glass ?denecking ( widening ) taken to extreme case, with HUGE materials growth quality results in the upper thicknesses.
There is some remote possibility this method might enable a debonding film transfer process akin to a Silicon SOI handle wafer process to possibly enable reuse of the expensive sapphire by a touch repolishing step, for now that is speculative.
I'd hazard that the statement "remains a laboratory curiosity" is out of place, aside from IP this method is likely to have very rapid uptake from potential licensees. The upper film quality looks orders of magnitude better than conventional films, likely leading to huge increases in potential power / efficiency with modest cost over crappy films.
This bears very close watching how fast industry uptake proceeds.
Interestingly incredible assertion based on a guess remains a laboratory curiosity. If the depo process yields LEDs and other devices with consistently reproducible results we can look forward to brighter solid-state lighting. It certainly bears following results of the new films.
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