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UK cracks GaN-on-silicon LED issues

A government-backed LED project produces crack-free GaN-on-silicon epiwafers with an internal quantum efficiency of 40 percent.

A UK-based £3 million ($5.5 million) development program seeking to slash LED production costs has overcome the hurdle of managing the strain resulting from GaN-on-silicon epitaxy.

"We have succeeded in growing LED structures on 6-inch silicon that are completely free of cracks," says Colin Humphreys from the University of Cambridge.

This research team has reduced strain by inserting interlayers and monitoring the growth in-situ with a Laytec Epicurve tool.

The interlayers also helped to cut dislocation density and ultimately boost internal quantum efficiency (IQE) to 40 percent.

"That's still not good enough, but it is almost good enough," remarks Humphreys, who points out that blue-emitting GaN-on-sapphire LEDs produce an IQE of about 70 percent.

Humphreys says that the project could cut GaN LED manufacturing costs by a factor of four to ten.

"There are two reasons for the cost saving," explains Humphreys. "One is that a 6-inch silicon wafer costs something like $15, so it's a lot cheaper than even a 2-inch sapphire wafer."

But he says that the main saving is access to 6-inch silicon processing lines that have very low processing costs.

After Humphreys team has optimized its process, defense technology company Qinetiq will fine-tune the technique to improve reproducibility.

US assistance
When the project kicked-off, Filtronic had been given the role of implementing the process developed at Qinetiq for high-volume manufacturing.

In the meantime the fab at Filtronic s Newton Aycliffe facility has been bought by GaAs giant RF Micro Devices, but it appears that the US manufacturer is keen to continue with the project.

As a government-funded effort that might ultimately generate profits for an overseas company, this might be viewed as poor use of the UK s public purse. However, Humphreys believes that the effort will still benefit the UK economy.

"The growth equipment will be in county Durham, so it will be jobs for the UK," he remarked. "New semiconductor manufacturing in the UK would be fantastic."

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