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The surest way to make light emitting diodes that are efficient and bright is to fabricate them on a substrate made of the same material as the LED itself.
So says LED maker Soraa Inc. in Fremont, Calif. The company produces LEDs that it claims emit more light per unit area than any other LED and handle more electric current per area than any other LED. Soraa gets this kind of performance by building the LEDs on a substrate consisting of GaN. This differs from the usual practice of building LEDs on top of either sapphire or SiC, materials that are cheaper than GaN and which are compatible with it. The problem with these substrates is that they can induce imperfections in the LEDs grown on top and these imperfections reduce the amount of light the LED can generate.
“Because we use a GaN substrate, we don’t have such issues as wafer strain, wafer bowing because of the strain, and (crystal) dislocation densities that arise because of different substrates,” says Soraa CTO Mike Krames. “That allows a higher quality crystal material which leads to higher performing devices.”
The LEDs made this way also are more efficient. “We have been able to engineer the layers on the native substrate to create an active layer stack that runs at high efficiencies and current densities, several factors higher than standard LEDs that are fabricated on foreign materials,” says Krames. “We get many more lumens per wafer. This brings dramatic benefits in lowering overall LED cost and in higher brightness.”
Soraa’s first product to use GaN substrates is an LED replacement for a 50W halogen that only consumes 12 W. A point to note is that the lamp uses only passive cooling. “Other companies that are doing this have to use tricks like fans to cool the LED and get enough power,” says Krames. “Our lamps also use just a single LED rather than an LED array found in competing devices. This lets them produce a single clean beam with a single shadow rather than a multishadowed beam which some consumers dislike,” Krames says.