Plessey Semiconductors is leveraging its proprietary GaN-on-Si epitaxial process technology to produce LEDs on its 6-inch line at its factory in Plymouth, England.
Plessey announced early this month that samples of its LED products using gallium nitride films on 6-inch silicon substrates are now commercially available -- an industry first. Other companies, including Toshiba and Bridgelux, have announced efforts on GaN-on-Si LEDs, but have not yet reached commercial production.
(Source: Plessey Semiconductors)
The use of Plessey's MAGIC (Manufactured on GaN I/C) line using standard semiconductor manufacturing processing provides yield results above 95 percent and high-volume processing times, providing a strategic pathway for the cost-competitiveness of LEDs compared to more expensive solutions based on sapphire and silicon carbide.
Interestingly, Plessey only acquired its first metal-organic chemical vapor deposition (MOCVD) reactor in August 2012, prior to generating the first production material in April. Sensibly, these LEDs will be targeted to lower-performance applications such as electronic indicating and accent lighting. However, Plessey's breakthrough of commercial GaN-on-Si LEDs did not materialize overnight: It was the fruit of a decade-long collaboration with Cambridge University in England.
The crystal structure of gallium nitride makes it a near-perfect lattice match for growth on silicon carbide -- and, to a lesser extent, sapphire. In comparison, silicon is a worse choice based on the crystalline lattice mismatch. But silicon, by virtue of being the substrate of choice for semiconductor devices, offers the advantages of higher abundance, higher quality, lower cost, and a more expansive supply chain.
In 2003, materials professor Sir Colin Humphreys and his team began research in this field and eventually developed a successful process, which is now the basis for Plessey's GaN-on-Si LED production. In addition, Plessey hired several of Humphreys's post-doctoral scientists to ensure a smooth transfer of the technology to their factory.
The GaN growth at the Cambridge facility uses a 6" x 2" Thomas Swan (Aixtron) reactor; however, Plessey is now using a more production-worthy Aixtron CRIUS II-XL 7" x 6" platform. Cambridge recently upgraded its facility with new tools funded by the Engineering and Physical Sciences Research Council in England.
Still lower costs in prospect
One of the main issues stalling the wide-scale adoption of LEDs for general indoor and outdoor lighting is the technology's higher cost compared to more conventional alternatives. The new GaN-on-Si growth reactor at the University of Cambridge is poised to enable researchers to improve further a method of growing low-cost LEDs on silicon substrates, with the goal of reducing their cost by more than half. The Cambridge team believes it can optimize its current technology ultimately to achieve an 80-percent cost reduction in 48W LED bulbs.
Furthermore, the US Department of Energy has funded numerous university and corporate initiatives over the last five years, focused on reducing the cost of solid-state lighting. These funds include millions of dollars in the US's stimulus program to help lift the economy out of recession in 2009.
Plessey is focused on improving output efficiency and has stated it is on schedule for further improvements in light output throughout this year. Its strategy makes sense: to improve technology and product performance gauged for lower-performance LED applications such as indicators, while generating revenue to enable it eventually to meet the more aggressive benchmarks required by more demanding applications.