LEDs are about four times more efficient than incandescent lights, last an estimated 15 years, and contain no harmful mercury as do compact fluorescent lights bulbs. It’s estimated that if everyone switched to LEDs for lighting, the world’s electricity consumption would drop by 10%. But until now, LEDs had to be made on a substrate of sapphire, a process that makes them expensive. Researchers at Purdue University have developed a technique that builds LEDs on a substrate of low-cost, zirconium nitride-coated silicon. Ordinarily, ZN is unstable in the presence of silicon. Purdue engineers solved this problem by putting an insulating layer of aluminum nitride between the silicon and ZN. ZN serves as a reflector, making sure all the light generated by the gallium nitride in LEDs gets sent in the same direction. In sapphire-based LEDs, manufacturers must add a reflecting layer after constructing the light emitting portion of the LEDs. The sapphire technique also doesn’t lend itself to mass production.
The new silicon method of making LEDs, on the other hand, will let manufacturers produce hundreds, perhaps thousands of LEDs on a single silicon wafer. Silicon also dissipates heat better than sapphire, which should make for more reliable, long-lasting LEDs. In all, the new technique should lower the cost of an LED to 5% or less of its current cost. The researchers expect affordable LEDs to be on the market in two years even though they still have two hurdles to overcome. They must prevent the gallium nitride layer from cracking as the silicon wafer cools after manufacturing, and they need to improve the yield rate of the overall manufacturing process.