As Plessey Semiconductor scales up commercial GaN on silicon LED production, where next for the UK technology pioneer, asks Compound Semiconductor.

High quality growth of LEDs on silicon is difficult but with IP from Cambridge University spin-off CamGaN, UK, Plessey is delivering commercial grade products.

In April this year, UK-based semiconductor manufacturer, Plessey Semiconductor, sampled the industry's first commercially available GaN on 6-inch silicon LEDs amid claims of a massive capacity ramp.

As promised, a raft of new, higher power LEDs has just been released and company executives have told Compound Semiconductor to expect much more.

In the coming months, even higher power LEDs will be up for grabs, with the company then supplying its GaN on silicon LEDs for incandescent replacement lamps next year. Come mid-2014, the company intends to move up the supply chain and, with an existing strategic partner, build lighting products, as well as LEDs. And by the end of that year, plans to install ten MOCVD reactors at the company's facility in Plymouth should be well underway. The intentions are ambitious; can Plessey really deliver?

“Releasing the entry level product generated a lot of interest in our LEDs particularly for backlighting and indicator applications, and other custom LED designs,” explains chief operating officer, Barry Dennington. “Customers have been interested in the GaN on silicon technology – it gives significant cost benefits – and that has opened up opportunities for us to quote new LEDs in the consumer space as well as signage.”

“There are literally hundreds of different customer requests and market applications, it's a case of picking the right opportunity,” he adds.

Right now, the company is intent on demonstrating higher efficiency and higher power GaN on silicon LEDs. The initial, entry level LEDs delivered only a few lumens for low drive currents, targeting indicating applications. However, the latest 2mm², blue versions deliver 350mW when driven at 420mA - a leap from the entry level devices - and are making in-roads to solid state lighting applications.

This move beyond what some have called the first 'proof-of-concept' devices, places the UK LED manufacturer ahead of the competition, for now. While other companies such as Bridgelux and Osram have showcased GaN-on-silicon LEDs with lumens per Watt outputs of more than one hundred in the laboratory, where are the commercial products?

“We hear companies are getting to those sorts of levels but whether or not they are in production is questionable,” says Keith Strickland, chief technology officer at Plessey.

The CTO is certain his company will have delivered a 70 to 80 lm/W device by the end of this year, and as Dennington says: “Next year we will also have an LED product capable of competing in the incandescent lamp replacement market, and with relatively few LEDs compared to what is on the market today.”

Indeed, as part of the European “Consumerizing Solid-State Lighting” programme, led by Philips, Plessey supplied the GaN on silicon LEDs that lit up the project's $9.95 lamp intended to replace the 60 W incandescent bulb.

“We've demonstrated our capability to do this through the CSSL European programme... and we are confident that if you look at the breakdown of the costs for these lamps, we will meet or beat cost targets by virtue of the GaN on silicon process and economies of scale from six inch manufacturing,” he adds.

Which brings Plessey to the next milestone on its roadmap; vertical integration. Having provided the LEDs for tomorrow's cheap incandescent replacement LED lamp, executives at Plessey believe vertical integration towards lighting would be pretty straightforward. As Dennington highlights, his researchers have mastered LEDs, a key part of the lamp, and the company already employs lighting as well as optical engineers.

“We think its a relatively easy step to move into producing lamps and we have at least four projects that could see Plessey producing lighting products in the second half of next year,” he says. “This would give us an opportunity to be more vertically integrated in the market and offer a broader range of lighting solutions to customers, not just LED components.”

Rapid expansion

So as Plessey continues to drive LED performances forward - performances don't yet match those of sapphire-based favourites - the appeal of GaN-on-silicon LEDs for the lights of tomorrow will only increase. Relatively cheap, available silicon wafers twinned with fabrication on depreciated CMOS lines, makes manufacturing on large-size wafers more and more irresistible to manufacturers, and this is what the company is banking on.

The business is looking to increase its Plymouth-based fleet of MOCVD reactors from one to ten, but with each reactor costing some $2.5 million, is this really viable? Both Dennington and Strickland think so.

As Strickland points out, the Plymouth facility has a lot of room for expansion and while this will require significant investment, the company plans to do just this.

“This expansion is driven by customer demand so we have to be successful in getting our products from the roadmap to the market,” adds Dennington. “But we have the right kinds of partners... and we are bringing in equipment to improve yields and throughputs so clearly the next step is to ramp up the number of reactors we have.”

And with each reactor capable of churning out 2 million, 1mm2 die every week, the potential increase in output rates is breathtaking. But despite the rapid ramp in manufacturing, the company will be maintaining manufacturing in the UK, and the UK alone.

“We have no plans right now to take the technology outside the UK,” concludes Dennington. “It's still a very disruptive breakthrough technology and our IP is very precious to us. We need to manage any outsourcing outside the UK very carefully; it could be considered with the right partner but we are very cautious right now.”



Plessey's LEDs are grown on six inch silicon wafers with an AlN nucleation layer and complex structure and layers of AlGaN, GaN and SiN preventing wafer bowing and reducing dislocation density.

Read more at "Plessey slashes LED costs"  http://www.compoundsemiconductor.net/csc/features-details/19735992/Plessey-slashes-LED-cost.html