GaN LED chips on silicon wafers

Researchers at Osram Opto Semiconductors have manufactured blue and white LED prototypes in which the light-emitting gallium-nitride layers are grown on silicon wafers with a diameter of 150 mm. The wafers replace the sapphire substrates commonly used until now, with no loss of quality. Already in the pilot stage, the chips are being tested under practical conditions, meaning that the first LEDs on silicon from the company could hit the market in two years.

Silicon is an attractive and low-cost option for the lighting markets of the future. Due to its already widespread use in the semiconductor industry, the availability of large wafer diameters and its very good thermal properties silicon is a low-cost option for large-volume fabrication. Quality and performance data on the fabricated LED silicon chips match those of sapphire-based chips. The blue UX:3 chips in the company’s standard Golden Dragon Plus package achieve a brightness of 634 mW at 3.15 V, equivalent to 58% efficiency.

These are good values for 1 mm² chips driven at 350 mA. In combination with a conventional phosphor converter in a standard housing - in other words as white LEDs - these prototypes correspond to 140 lm at 350 mA with an efficiency of 127 lm/W at 4500 K.

It is already possible to fabricate over 17,000 LED chips of one square millimetre in size on a 150 mm wafer. Larger silicon wafers could increase productivity even more; researchers have already demonstrated the first structures on 200 mm substrates.