GaN-on-GaN breakthrough LED boosts MR16 performance
Margery Conner - May 30, 2012
Despite the ever-improving light output from white LEDs, there are still some fundamental limitations in the current technology, which in general is based on either silicon carbide substrates (Cree) or sapphire substrates (just about everyone else). The active or light-emitting region in a white LED is formed by growing gallium nitride (GaN) on the substrate.
The problem with this approach is that the crystal lattice mismatch caused by the two different materials results in imperfections, and these imperfections in the LED reduce the amount of the light the device can produce.
A Fremont, CA start-up, Soraa, has developed the technology to grow GaN crystals on their native GaN substrate so that the active-GaN-region crystals grow with fewer imperfections and can accommodate higher power densities which, the company claims, allows the LED to emit 5-10 times more light from the same crystal area.
Transmission electron microscope images show multiple dislocations in conventional GaN material on the left, and dislocation-free GaN-on-GaN crystals on the right.
Soraa has an impeccable pedigree: One of its founders is Shuji Nakamura, who is credited with the discovery of p-type doping in GaN and thus the development of blue, green, and white LEDs.
Interestingly, the company’s first product is not an LED but rather a complete LED MR16 lamp. Soraa argues that, while politicians have been focused on the demise of the incandescent A-lamp, the MR16 actually has a wider range of markets and applications. Europe, for example, currently uses over 1 billion MR-16 lights, which are small 35-50W halogen lights, about 2 inches long, and costing about $12 each.
Cree certainly sees the importance of this market: Last year it introduced a new, smaller-sized LED array targeted specifically for use in MR16s. The challenge was to get enough LEDs into an array to re-create the intense point source of the tiny halogen lights, while still keeping the warm color characteristics. Cree’s MT-G array crams 12 LEDs into a 9.1mm2 package. However, while these arrays are an improvement, they still can’t replicate the point-source performance of halogen. Shadows aren’t sharp, and the light focus is limited because of the large source area.
This is where Soraa’s GaN-on-GaN-enabled 12V AC product family shines: Depending on the version, the product family’s performance approaches that of generic 50W halogen lamps, including crisp shadows and similar CRI. The lamps include integral drivers that operate with several combinations of transformers and dimmers. The standard version is offered at either 2700K or 3000K and 80 CRI, and a high-CRI version is available at 95 CRI. To reach high color-rendering with deep red (R9>90) this version uses a violet-pumped triphosphor for a closer match to the blackbody than can be achieved with conventional blue-pumped two-phosphor technology.
Soraa made its initial announcement at Strategies in Light in February, and was demonstrating its products with four different lamps in its MR16 family at LightFair earlier this month.
(I’m still puzzled as to why Soraa isn’t offering its LEDs in component form, but I would never, ever bet against Shuji Nakamura.)