9 August 2011

Bridgelux raises GaN-on-Si LED efficiency record

LED chip and lighting array maker Bridgelux Inc of Livermore, CA, USA (which claims to be the only vertically integrated maker of LED solid-state light sources specifically for the lighting industry) says that it has raised its previous industry record for luminous efficiency (lumen per Watt) for gallium nitride on silicon (GaN-on-Si) LEDs.

In March, Bridgelux demonstrated GaN-on-S-based LED technology exhibiting luminous efficacy of 135lm/W at a correlated color temperature (CCT) of 4730K (using a single 1.5mm-diameter power LED operated at 350mA), representing what was claimed to be the industry’s first commercial-grade performance for a silicon-based LED. The LEDs had very low operating voltages, requiring just 2.9V at 350mA and <3.25V at 1A.

Bridgelux says that it has now demonstrated performance levels comparable to state-of-the-art commercial sapphire-based LEDs. Cool-white LEDs showed efficiencies as high as 160lm/W at a CCT of 4350K. Warm-white LEDs constructed from the GaN-on-Si chips delivered 125lm/W at a CCT of 2940K and a color rendering index (CRI) of 80. 

Encapsulated 1.5mm blue LEDs emit 591mW with wall-plug efficiencies as high as 59% at 350mA, exceeding any published values it is claimed. The LEDs have very low forward voltages, 2.85V at 350mA, suiting use at high current densities. At a drive current of 1A the LEDs emitted 1.52W of blue power at a forward voltage of 3.21V, resulting in a wall-plug efficiency of 47%.  Wavelength uniformity of sigma 6.8nm has been demonstrated for 8-inch LED wafers with a median wavelength of 455nm.

Conventional LEDs are made using sapphire or silicon carbide (SiC) substrates as the starting material. Both are more expensive than silicon, so production costs have inhibited the widespread adoption of LED lighting in homes and commercial buildings, says Bridgelux. But growing GaN on larger, low-cost silicon wafers that are compatible with high-volume semiconductor manufacturing can deliver a 75% improvement in cost over existing approaches, says the firm. Bridgelux reckons that its technology process has the potential to significantly drive down the cost of manufacturing LEDs and make them competitive with conventional white lighting technology. 

One problem is that the thermal expansion coefficient of GaN is considerably larger than that of silicon. This mismatch can cause the epitaxial films to crack, or the wafers to bow, either during epitaxial growth or at room temperature. However, Bridgelux says that its proprietary buffer layer process produces crack-free wafers that are virtually flat at room temperature. Using its proprietary buffer layer technology, Bridgelux has demonstrated growth of crack-free GaN layers on 8-inch silicon wafers, without bowing at room temperature, improving the performance and manufacturability of GaN LEDs on silicon substrate.

“These achievements are a direct result of our investment in building a world-class team of Bridgelux materials scientists and chip design engineers with a strong focus on driving industry-leading epitaxial process technology,” says chief technology officer Dr Steve Lester. “We will continue to aggressively develop our GaN-on-Si processes in order to drive the migration of LED commercial production from sapphire to silicon substrates,” he adds. “Our first commercially available GaN-on-Si products remain on schedule for delivery to the market within the next two years.”

“This new technological breakthrough is a direct result of Bridgelux’s continued investment in R&D combined with a singular focus on the needs of the solid-state lighting market,” says CEO Bill Watkins. “This key innovation is a game-changer for the industry, delivering dramatic reductions in the up-front capital investment required for solid-state lighting and thereby significantly increasing the rate of market adoption,” he adds.

Bridgelux, which maintains an asset-light operating model, aims to leverage its R&D and intellectual property position in LED epitaxy to to pursue partnerships with existing semiconductor manufacturers. Using existing semiconductor fabs via partnerships with established semiconductor manufacturers has the potential to favorably impact production costs, margins and returns on invested capital, it reckons.  

See related items:

Bridgelux claims first commercial-grade performance for Si-based LED

Bridgelux raises $60m in equity financing round led by Craton

Tags: Bridgelux LEDs

Visit: www.bridgelux.com