GaN LEDs grow on silicon substrate

Researchers at Osram Opto Semiconductors say they have manufactured high-performance blue and white LED prototypes by growing light-emitting gallium-nitride layers on silicon wafers with a diameter of 150 mm (about 6 in.).

The Osram process: 1, Epilayer growth on silicon substrate. 2, Mirror and contact formation. 3, Transfer to silicon carrier and substrate removal. 4, Final chip processing.

The feat is noteworthy in that most LEDs are grown on sapphire substrates, rather than on silicon, because of compatibility issues between the silicon and the gallium. Silicon is a much less expensive substrate than sapphire and thus is more desirable for high-volume LED work. Osram says the wafers replace the sapphire substrates with no loss of quality.

Osram says the first LEDs on silicon from could hit the market in as little as two years. The GaN chips were fabricated using Osram’s thin-film UX:3 process, which involves transfer to a silicon carrier and removal of the original silicon substrate. The blue UX:3 chips so made hit a record optical power of 634 mW at 3.15 V, equivalent to 58% efficiency. When combined with a conventional phosphor converter in a standard housing to generate white light, the prototype LEDs generated 140 lm at 350 mA with an efficiency of 127 lm/W at 4,500K.

Says Dr. Peter Stauss, project manager at OSRAM Opto Semiconductors, it is already possible to fabricate over 17,000 LED chips of one square millimeter in size on a 150-mm wafer. Researchers have already demonstrated the first structures on 200 mm substrates (about 8 in.).

“Stress tests we've already conducted demonstrate the high quality and durability of the LEDs, two of our traditional hallmarks,” he added.

More info: www.osram-os.com