Bridgelux has boosted the performance of its experimental light-emitting diodes (LEDs) grown on silicon wafers and said it will start delivering them to the market within two years.
If Bridgelux can keep on track, its silicon LEDs could dramatically cut the cost of solid state lighting: LED chips account for 60 percent or more of the cost of a bulb. It’s not a done deal -- manufacturers have tried to grow LEDs on silicon for years without much success -- but if it works, Bridgelux could establish a strong foothold in the market.
Silicon LEDs emitting a cool white light showed efficiencies of up to 160 lumens per watt, while warm white LEDs made on the same process emitted up to 125 lumens per watt. In March, the company trotted out a prototype that emitted 135 lumens per watt.
Just as important, the LEDs were grown on an eight-inch silicon wafer, a smaller wafer for the computer and memory industry but a behemoth for LEDs. The wafer and the substrates didn’t crack or bow.
LEDs are essentially finely tuned crystals of gallium nitride grown on top of wafers made of sapphire or silicon carbide. The epitaxial process of growing the gallium nitride is complex and the wafers aren't cheap. Most LED producers currently grow their LEDs on wafers measuring only two to four inches. Bridgelux, in fact, grows its LEDs on two-inch wafers. Large LED makers like Osram are only now in the midst of shifting to six-inch wafers. Sapphire wafers measuring eight inches across may never occur.
Silicon wafers are far cheaper than sapphire or silicon carbide. More importantly, there are literally thousands of fabrication facilities around the world that can produce eight-inch silicon wafers and that are currently running at half speed or producing fairly low-end components. The semi industry already graduated to larger 12-inch wafers. Bridgelux's, in fact, uses an old silicon fab in the Valley.
"This is the holy grail. This is why all of the big semi guys like Samsung, LG and Toshiba are looking at LEDs," Bridgelux CEO Bill Watkins told us earlier this year. "The problem for the semi guys is that they don't know how to do it yet."
These silicon LEDs could cost 5 cents or less per unit, compared to 35 cents to 45 cents for a conventional chip, and could cut the price of LED bulbs by $7.50 or more.
Bridgelux will make the chips, but will also likely enter into joint ventures and licensing arrangements with established manufacturers.
The breakthrough is possible because of a proprietary buffer layer.
Bridgelux is in the midst of a fifth round of funding. It has raised $180 million to date.