This represents, said the company in its press release, the “industry's first commercial-grade performance for a silicon-based LED.”
Bridgeglux said that the 135 lm/W performance was achieved at a CCT of 4730K using a single 1.5-mm power LED operated at 350 mA. The LED had an extremely low operating voltage, requiring just 2.90V at 350 mA and less than 3.25V at 1A.
Let’s put this in context; first, this is of course an R&D result, and there is no indication of yield, uniformity or substrate size. Bridgelux faces a long and complex challenge to translate this result into a commercially viable process on large-diameter (8-inch) silicon substrates. The company said that it “anticipates the delivery of its first commercially-available GaN-on-silicon products over the course of the next two to three years.”
Also the chip size is significant, since it is usually easier to demonstrate higher efficacy when the chip size is larger and the current density is lower. However, the 135 lm/W number is impressive, and the company points out that this performance is comparable to state-of-the-art sapphire-based LEDs available 12-24 months ago.
Also, just for clarification, these are not “silicon-based” LEDs – the light comes from the GaN-based materials grown on top of the silicon wafer, not from the silicon itself. The light-emitting GaN-based structure is similar to today’s GaN-based LEDs which are grown on sapphire or silicon-carbide substrates as the starting material. But large-diameter sapphire and silicon carbide substrates are costly, difficult to process, and not widely available, says Bridgelux.
However, growing GaN on larger, low-cost silicon wafers that are compatible with modern semiconductor manufacturing can deliver a 75% improvement in cost over current approaches, claims Bridgelux. Optimization of the epitaxy process on 8-inch Si wafers will make LED manufacturing compatible with existing automated semiconductor lines.
Bridgelux maintains an “asset-light operating model” and says that it will leverage its R&D and intellectual property position in LED epitaxy to jointly manufacture GaN-on-silicon LEDs.
The company says it is currently in discussions with a number of established semiconductor companies regarding the utilization of the many fully-depreciated 8-inch semiconductor fabrication operations available around the globe.
Bill Watkins, Bridgelux CEO, said: "The significantly reduced cost-structures enabled by silicon-based LED technology will continue to deliver dramatic reductions in the up-front capital investment required for solid-state lighting. In as little as two to three years, even the most price-sensitive markets, such as commercial and office lighting, residential applications, and retrofit lamps will seamlessly and rapidly convert to solid-state lighting."
Bridgelux says that its R&D team, led by Steve Lester, has been investigating GaN-on-silicon technology for the past five years. Other companies are also developing similar technology. A Wall Street Journal blog article said that Bridgelux thought its announcement “is dramatic enough to force others to disclose their progress.” The article also quoted Watkins as saying: “This will shake everybody out.”