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LED chip makers lock horns in Vegas

The "city of sin" saw leading chip makers go on the offensive with claims of class-leading devices, and GaN-substrate developers championing breakthroughs in large-diameter free-standing material. Richard Stevenson reports from the 7th International Conference on Nitride Semiconductors.

by Richard Stevenson in Las Vegas, Nevada
Chip makers Nichia, Lumileds, Cree, Seoul Semiconductor and SemiLEDs all expounded the virtues of their latest GaN LED technology at the 7th International Conference on Nitride Semiconductors, being held this week in Las Vegas.

Nichia s Yukio Narakawa kicked-off the day by announcing the development of a 1 mm x 1 mm white LED delivering 169 lm/W efficacy at 20 mA. This beats the 161 lm/W figure that Nichia reported last year, and resulted from research to improve current spreading and reduce the forward voltage.

The latest LED also offers improved performance at high drive currents, according to Narakawa. It produces 134 lm/W at 350 mA and a forward voltage of 3.1 V, and can deliver 361 lm at 97 lm/W when driven at 1 A.

Philips Lumileds best result at 350 mA still stands at 115 lm/W. This was the value announced earlier this year for its "droop-free" 1 mm x 1 mm chip, which features a double heterostructure design incorporating a thick InGaN region.

Frank Steranka, who was speaking on behalf of Lumileds, pointed out that by increasing the size of the chip, this LED can deliver higher efficacies. A 4 mm x 4 mm LED emitted 142 lm/W.

Cree s John Edmond said that the Durham chip maker s best result was 133 lm/W at 350 mA, the same value announced last week (see related story). This chip is also bigger than 1 mm x 1 mm, although Edmond did not disclose its exact dimensions.

Meanwhile, SemiLEDs, the Taiwanese chip maker that incorporates a metallic mirror into its emitters, revealed that it had also reached the 100 lm/W efficacy milestone at 350 mA. The higher efficacy comes from adding a several-micron-wide step to the textured surface of the LED structure.

Seoul Semiconductor CEO Chung Lee championed the Korean company s "Acriche" product line. Although these devices "only" operate at 60 lm/W, they run directly from an AC source, which Lee sees as a key advantage.

Keeping to the DOE roadmap
Lumileds Steranka also discussed the advances required to hit the US Department of Energy s stiff future targets, which include reaching 150 lm/W at 2 A by 2012.

According to him, to hit this particular milestone will require a hike in internal efficiency to 90%. Phosphor technology must also improve, as one fifth of the emission can be lost in conversion.

Although the 2012 target is demanding, Steranka believes that hitting this goal holds the key to LED adoption in solid-state lighting.

At present, the cost-per-lumen for incandescent and fluorescent lamps are $0.03-0.05 and $0.06, respectively. To compete, the corresponding figure for LEDs needs to drop by a factor of 20.

But increasing the drive current to 2 A and efficacy to 150 lm/W will deliver a nine-fold improvement. If the cost of making these improved LEDs can also be halved, then chip manufacturers will be in the right ballpark.

Richard Stevenson is features editor at Compound Semiconductor magazine.

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