On July 17, 2008, Purdue University made this exciting announcement. By replacing traditional lighting with solid state lighting technologies such as LED, electricity consumption can be reduced by 10%. LED is also more friendly toward the environment as it does not contain mercury, a poisonous substance that make up CCFL technology that is being touted as more green than incandescent bulbs. The complete findings from Purdue University can be founded in this month’s Applied Physics Letters journal that is published by the American Institute of Physics.
Sapphire substrates are expensive. And that’s what LEDs are manufactured from. Thanks to a major breakthrough by Purdue University researchers, LEDs can now be manufactured on metal-coated silicon wafers that are have much lower costs. Although adoption of LEDs in general lighting as well as a backlight for LCDs have been enthusiastic, the cost of LEDs cannot be ignored as they are quite a bit more expensive, about 20x, than incandescent and fluorescent lighting technologies. The reason why sapphire-based LEDs are so much more expensive is the requirement of “a separate mirror-like collector to reflect light that ordinarily would be lost.” Purdue engineers were able to develop a built-in reflective layer made of zirconium nitride by “metallizing” the silicon substrate.
Zirconium nitride normally undergoes a chemical reaction and changes its properties in the presence of silicon. Purdue researchers used a method called reactive sputter deposition to develop an insulating layer of aluminum nitride between the silicon substrate and the zirconium nitride that stabilizes the zirconium nitride. Zirconium and aluminum metals were bombarded with positively charged ions of argon gas. The metal atoms reacts with nitrogen in the vacuum chamber resulting in the deposition of aluminum nitride and zirconium nitride unto the silicon surface. Gallium nitride is then deposited via organometallic vapor phase epitaxy in a chamber at around 1000 degrees Celsius. Epitaxial growth is achieved when zirconium nitride, aluminum nitride and gallium nitride are deposited on the silicon.
[tags]Purdue University, LED, Light Emitting Diode, Solid State Lighting, Gallium Nitride, Sapphire-Based LED, Zirconium Nitride, Zirconium Nitride Reflective Layer, Aluminum Nitride, Reactive Sputter Deposition, Argon Gas, Organometallic Vapor Phase Epitaxy[/tags]