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SemiLEDs Reveals 6-inch GaN LED Progress

Collaboration with Aixtron shows promise, but sapphire substrate prices must fall below $300 for volume production to become feasible.

SemiLEDs has successfully produced blue LEDs on 6-inch diameter sapphire wafers for what it and deposition equipment supplier Aixtron say is the first time.

But despite the joint effort s promising results and significant yield benefits, SemiLEDs does not currently have any plans to upgrade its Taiwan production lines to the larger format.

“We are in an R&D phase and will not plan for production until we can secure low-cost 6-inch sapphire," said Chuong Tran, president and chief operating officer of SemiLEDs.

“The price of 6-inch would have to drop down to about $300 per wafer to be attractive," he told compoundsemiconductor.net.

Tran indicated that the 6-inch sapphire substrate market is still in an early stage. SemiLEDs will have to work hard with suppliers to guarantee enough wafers of sufficient quality to use in production.

As SemiLEDs production process involves removing the sapphire layer and replacing it with a copper substrate, Tran suggests that his company could recycle substrates to help solve this issue.

Perhaps unsurprisingly, the first LEDs produced on a 1000 µm-thick 6-inch substrate are not up to the standard of the 4-inch GaN-on-sapphire wafers that SemiLEDs produces in large volumes.

“Characteristics of devices from 4-inch wafers are better than those from 6-inch, however I don t see why we cannot improve further," Tran said.

Converting an AIX 2800G4 MOCVD reactor like the one that SemiLEDs used to make the 6-inch wafers is extremely simple, Aixtron says, leaving general process conditions unchanged.

The Aachen, Germany, based company does however point out that larger wafers show a tendency to bow that must be controlled.

“We have found ways to do this, including appropriate in-situ monitoring," explained Rainer Beccard, Aixtron s vice-president of marketing.

Beccard says that the 6 x 6-inch configuration used in this joint demonstration is already well established in GaN electronics manufacturing, in particular for use with silicon substrates.

“For LEDs, most of our customers are still using 2-inch, while they get prepared for 4-inch," he said. “6-inch is the next step."

This trend is largely driven by the production-yield benefits offered by the bigger format.

Changing the AIX 2800 G4 from 42 x 2-inch wafers to 6 x 6-inch increases the total substrate surface area it can accommodate by approximately 30 percent. Furthermore, the proportion of the overall area at the edges of the wafers, which tends to produce fewer good die, is much lower with larger wafers.

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