Plessey Semiconductors has announced earlier this month that samples of its LED products using gallium nitride (GaN) films on 6-inch silicon substrates are now commercially available for sampling, which is the first of its kind across the industry. The development of comparable quality LEDs on silicon substrates to current standards is considered a holy grail for the LED lighting industry. Plessey is leveraging its proprietary GaN-on-Si epitaxial process technology to produce the LEDs on its 6-inch MAGIC (Manufactured on GaN I/C) line at its Plymouth, England facility. The use of Plessey’s MAGIC GaN 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 sapphire and silicon carbide-based solutions.
Interestingly enough, Plessey only acquired its first metalorganic chemical vapor deposition (MOCVD) LED film growth reactor in August 2012 prior to generating their first production material in April, which will be geared sensibly toward lower performance applications such as electronic- indicating and accent lighting. However, its technical progress on GaN-on-Si LEDs did not materialize overnight, no pun intended. 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 degree, sapphire. In comparison, silicon is a worse choice based on the crystalline lattice mismatch, but it offers the advantage of a higher abundance commercially, higher quality, lower cost and more expansive overall supply chain due to it being the substrate of choice for the majority of semiconductor devices.
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 the British manufacturer, Plessey’s GaN-on-Si LED production at its factory in Plymouth. In addition, Plessey hired several of Humphreys’ post-doctoral scientists to ensure a smooth transfer of the technology to their factory. The GaN growth at the Cambridge facility is using 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.
One of the main issues stalling the wide-scale adoption of LEDs for general indoor and outdoor lighting is the higher costs compared to more conventional alternatives. The new GaN-on-Si growth reactor at the University of Cambridge is poised to enable researchers to further improve a method of growing low-cost LEDs on silicon substrates, with the goal of reducing their cost by more than 50%. The Cambridge team believes it can ultimately achieve a technology platform to achieve even great cost-savings for 48W LED bulbs by optimizing its current technology. Furthermore, the US Department of Energy has funded numerous company and university research initiatives over the last five years under the Obama administration, focused on reducing the cost of solid-state lighting including several hundred million dollars in the country’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. It makes sense to improve its technology and product performance gauged for lower performance LED applications such as indicators, while generating revenue to eventually enable it to meet the more aggressive benchmarks necessary for high-brightness LEDs used in backlighting of high-definition TVs and general solid-state lighting. Other companies such as Toshiba and Bridgelux have announced efforts on GaN-on-Si LEDs but have not announced major progress or commercialization plans. The development of GaN-on-Si LEDs may also create spillover effects to elevate this material system for high-power or high-frequency devices as well.