Osram Opto Has Reported a Set of R&D Results From Gan LEDs Grown on Silicon

Prototype LEDs fabricated from GaN-based layers grown on 150-mm-diameter silicon substrates are similar in performance to standard production devices grown on sapphire. Osram Opto Semiconductors has reported a set of R&D results from LEDs fabricated using gallium nitride (GaN)-based layers deposited on silicon. The R&D devices made using GaN-on-Si material have performance levels that are similar to production devices fabricated on sapphire. Most GaN-based LEDs are grown on sapphire or silicon carbide substrates. While Osram Opto has already started moving its standard production of GaN-based LEDs to 6-inch (150-mm) diameter sapphire substrates, the real prize in moving to production on silicon wafers is the availability of larger, lower-cost substrates. The new LED chips are already in the pilot stage, and will be tested under practical conditions, says Osram, adding that its first LEDs fabricated on silicon could hit the market in just two years. "Our investments in years of research are paying off, because we have succeeded in optimizing the quality of the gallium-nitride layers on the silicon substrates to the point where efficiency and brightness have reached competitive market levels,” said Peter Stauss, project manager at Osram Opto Semiconductors. “Stress tests we've already conducted demonstrate the high quality and durability of the LEDs, two of our traditional hallmarks.” The GaN-on-Si 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 (see diagram). Blue UX:3 chips in the standard Golden Dragon Plus package achieved an optical power of 634 mW at 3.15V, equivalent to 58 percent efficiency. These are very good values for 1-mm2 chips at 350 mA. In combination with a conventional phosphor converter in a standard housing, prototype white LEDs produced 140 lm at 350 mA with an efficiency of 127 lm/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.” Mathematically speaking, it is already possible today to fabricate over 17,000 LED chips measuring 1-mm2 on a 150-mm wafer. Larger silicon wafers could increase productivity even more; researchers have already demonstrated the first structures on 200-mm (approx. 8-inch) substrates. The German Federal Ministry of Education and Research has funded some of Osram’s development work in the area of epitaxial growth of GaN-on-Si materials as part of its “GaNonSi” project network. Source: LEDs Magazine