Lattice Power demonstrates high-power InGaN LEDs grown on silicon

A Chinese LED start-up has demonstrated that InGaN-based LEDs grown on Si substrates by MOCVD can have similar performance to devices grown on conventional substrates.

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Lattice Power Corporation, an LED start-up company based in China, has demonstrated high-output white LEDs based on gallium nitride (GaN) die fabricated on silicon substrates.

Lattice Power has focused on developing GaN-on-Si MOCVD growth technology. The company, based in Nanchang, Jiangxi Province has demonstrated lab results of cool-white LEDs with an output exceeding 100 lumens at 350mA from a 1x1mm LED chip.

Most LEDs are fabricated by first depositing multiple GaN-based layers on top of a sapphire or silicon carbide (SiC) substrate. Silicon substrates offer potential cost advantages for LED growth, provided that problems with device performance can be ironed out.

Lattice Power is a 50-million dollar startup with investments from USA, Taiwan and Singapore, including major VC firms such as Mayfield, GSR Ventures, Asiavest and Tomasek. The company already has a small-die (200-micron) product for display applications in volume production.

The recent results for 1x1mm chips will be reported in a Late News paper at the ICNS-8 (8th International Conference on Nitride Semiconductors) conference, which takes place in Jeju Island, Korea, on October 18- 23, 2009 [see Footnote].

The results describe high-power, flip-chip, vertical-injection, thin-film blue and white InGaN/GaN LEDs grown on (111) Si substrates. In this case 2-inch Si substrates were used, although the company has also grown on 6-inch wafers.

Wafers were grown in an MOCVD reactor using a patented selective growth technique to control stress and cracking. Typically, growth of GaN-based layers on silicon results in cracking due to a mismatch between the coefficients of thermal expansion (CTE) between the different layers.

Lattice
White LED output
After epitaxial growth, the p-side of the wafer was metal-bonded (using an Ag alloy) to a carrier substrate. The original silicon substrate was then removed by wet acid etching. A more typical approach to making thin-film LEDs is to use laser lift-off from a sapphire substrate.

At 350mA drive current, a 1x1mm blue LED (453nm wavelength) achieved greater than 458mW output power. Also, a 0.5x0.5mm LED achieved 74.8mW output power at 60mA drive current.

By applying YAG phosphor, white LEDs made from 1x1mm chips have achieved 103lm at 350mA drive current, with a cool-white color temperature of 5130K and CRI of 69 (see graph). The device went through 500hrs of life-testing at 75°C board temperature and 900mA. Less than 5% degradation of light output was observed.

Lattice Power says that these results show that LEDs made from GaN grown on (111) Si substrates have great potential for practical commercial applications that can rival LEDs grown on sapphire and SiC substrates.

The company now plans to turn the 100-lumen device into a maufacturable product, and to introduce the 1mm and 0.5mm size products early 2010 to the general market.

Footnote:
If you are attending ICNS-8 and would be interested to write a report on the conference for LEDs Magazine, please contact us.

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