Light Emitting Diodes (LEDs) are more efficient than incandescent light bulbs, don’t pose the environmental hazards of compact fluorescent light bulbs (CFLs) and last about fifteen years.  Unfortunately, LEDs cost much more than either of the other alternatives.

Purdue University researchers have been working on ways to make LEDs affordable.  Timothy D. Sands, the Basil S. Turner Professor of Materials Engineering and Electrical and Computer Engineering and his graduate student Mark H. Oliver have developed a method of creating LEDs on metal coated silicon wafers which are tremendously cheaper than LEDs manufactured using a sapphire base.

Besides the basic cost, sapphire based LEDs use gallium nitrate as the light emitting substance which requires a separate mirror like collector to reflect light.  Purdue University researchers have solved this problem by adding a reflective zirconium nitride layer to the silicon substrate.  The zirconium nitride is actually added to an aluminum nitride insulating layer that keeps the zirconium nitride from reacting negatively with the silicon substrate.

In order to create the proper crystalline formation for the LED to work properly, requires a series of steps like “reactive sputter deposition” and “organometallic vapor phase epitaxy” to create “epitaxial growth“.  Boiled down these scientific terms mean that "the atoms travel to the substrate, and they move around on the silicon until they find the right spot."

Using Silicon allows multiple LEDs to be made from the same wafer, cutting costs and speeding up manufacture.  Silicon also dissipates heat more efficiently than sapphire, increasing the life span of the lights.

A few problems still exist with the process.  First, there is an unacceptably high level of defects and second, the gallium nitride layer is prone to cracking as the silicon wafer cools down.  Sands expects both of these problems to be solved shortly so that low cost efficient LEDs will be on the market in two years.

What does Sands consider low cost?  "When the cost of a white LED lamp comes down to about $5, LEDs will be in widespread use for general illumination," Sands said. "LEDs are still improving in efficiency, so they will surpass fluorescents. Everything looks favorable for LEDs, except for that initial cost, a problem that is likely to be solved soon."

Hmm.  Since I switched all of my light bulbs to CFLs about five years ago, I won’t be replacing them anytime soon.  However, when I do need a replacement, it is nice to know that LEDs should be a much more affordable and environmentally sound alternative.

Related:

Entry was posted on Thursday, July 17th, 2008 at 11:34 pm under Green Technology, Science and technology.

Read more entries by Susan Wilson.
Stumble It!