31 May 2007
Layers of InGaNP material are the key to brighter, cheaper high-brightness red LEDs, claims Quanlight, a spin-out of the University of California, San Diego.
US start-up company Quanlight says that its novel materials technology will improve the brightness, cost and wavelength-stability of red LEDs.
The firm, a spin-off from the University of California, San Diego (UCSD), has just won $3 million in venture capital, which it says will be enough to transition the company from the research and development stage to initial wafer production.
Quanlight's technology is based on a dilute nitride material system, explained CTO Vladimir Odnoblyudov: "The system is InGaNP, with a few percent of nitrogen [content]."
"It is pseudomorphically grown on a transparent GaP substrate, which eliminates the need for wafer bonding," he added.
Growing material pseudomorphically means that there is a slight mismatch between the GaP and InGaNP lattices, although not enough to generate problematic strain in the epiwafer.
Odnoblyudov told compoundsemiconductor.net that InGaNP has superior intrinsic properties to AlInGaP, the active material that is normally used in red, orange and yellow LEDs.
These properties include larger band offsets, and result in improved characteristics when compared with conventional devices, such as better wavelength stability, and increased brightness at high current densities and/or high temperatures, claims the CTO.
The dilute nitride approach has been developed for commercial use before, most notably in long-wavelength lasers for fiber-optic communications – albeit with limited success. But Odnoblyudov says that the Quanlight approach is different:
"MOCVD-grown InGaNAs material used up to 40 percent indium content to push the [laser] wavelength to 1.3 µm," he explained. "This resulted in high strain in the epitaxal layers, which degraded lifetime and reliability."
"In InGaNP, sufficiently lower indium concentrations are used, so these problems can be avoided."
In a recent Applied Physics Letters publication (see restricted link), Odnoblyudov and UCSD colleagues including Charles Tu described an MBE-based approach to InGaNP epiwafer growth, and subsequent LED chip fabrication.
However, to prepare for commercial LED production, Quanlight has been transferring the epitaxial growth process to an MOCVD platform and using 3-inch GaP substrates.
According to Elliot Hicks, director of operations at Quanlight, that transfer has gone smoothly, with all technical milestones being hit so far, and chip optimization now in progress.
The company has been working with conventional liquid encapsulated Czochralski (LEC) produced GaP material, although it is hoped that a collaboration with substrate specialist PVA Tepla will result in a vertical gradient freeze (VGF) process that can produce crystals with lower defect densities.
With the aid of the recent funding, Quanlight is now looking to complete the development of red LEDs by the end of this year, before switching to concentrate on yellow and amber emitters. Production of red LEDs is set to begin in early 2008. "Possible business models are licensing the technology or outsourcing the manufacturing," said Odnoblyudov. "Quanlight does not plan to go above the epiwafer level in the supply chain."
The latest venture round was led by Blackbird Ventures and (SHW)2 Enterprises. Blackbird CEO Neil Senturia also happens to be CEO of Quanlight.
Senturia is a serial entrepreneur, but appears to have plenty of other skills up his sleeve. His biography on the Blackbird web site says that as well as having sold technology start-up firms to the likes of Lockheed-Martin and Cisco Systems, he has worked in real estate, and was also a screenwriter for the classic army hospital sitcom M*A*S*H.