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Gallium nitride led chips on silicon in pilot stage

Researchers have successfully manufactured high performance prototypes of blue and white leds in which the light emitting gallium nitride layers are grown on silicon wafers with a diameter of 150mm.

According to a team from OSRAM Opto Semiconductors, the silicon replaces the sapphire commonly used without a loss in quality. Already in the pilot stage, the new led chips are to be tested under practical conditions, which could see them on the market in just two years.

Peter Strauss, project manager at OSRAM, said: "Our investments in years of research are paying off, because we have succeeded in optimising the quality of the gallium nitride layers on the silicon substrates to the point where efficiency and brightness have reached competitive market levels. Stress tests we've already conducted demonstrate the high quality and durability of the leds, two of our traditional hallmarks."

The company claims to have acquired 'comprehensive expertise' over the last 30 years in the process of artificial crystal growth (epitaxy), while the German Federal Ministry of Education and Research funds these activities as part of its GaNonSi project network.

OSRAM believes this is a pioneering development for several reasons. On account of its widespread use in the semiconductor industry, the availability of large wafer diameters and its good thermal properties, silicon is an attractive and low cost option for the lighting markets of the future. According to OSRAM, quality and performance data on the fabricated led silicon chips match those of sapphire based chips: the blue UX:3 chips in the standard Golden Dragon Plus package achieve a record brightness of 634mW at 3.15V – equivalent to 58% efficiency. In combination with a conventional phosphor converter in a standard housing (white leds) the prototypes respond to 140lm at 350mA with an efficiency of 127lm/W at 4500K.

"For these leds to become widely established in lighting, the components must get significantly cheaper while maintaining the same level of quality and performance," said Stauss. "We are developing new methods along the entire technology chain for this purpose, from chip technology to production processes and housing technology."

It is already possible today to fabricate more than 17,000 led chips of 1mm2 in size on a 150mm wafer. Larger silicon wafers could increase productivity even more; researchers have already demonstrated the first structures on 200mm substrates.

Author
Chris Shaw

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