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Think Green
Another group in the Future Chips Constellation has been funded by the Department of Energy’s Solid-State Lighting Core Technologies program to create brighter, more efficient light-emitting diodes (LEDs). Christian Wetzel, the Wellfleet Career Development Constellation Professor, and his team aim to close the “green gap” in LED technology by doubling or tripling the power output of green LEDs in three years.
Efficient green LEDs will make it possible for solid-state devices to produce white light with much better color rendering than current methods. Blue LEDs are in commercial products like cell phones, and by adding a layer of phosphor, products can be made to emit a white light. “That’s a feasible solution so far, but it’s not much better than a fluorescent tube in terms of color rendering,” says Wetzel. The more direct and more efficient path would be to make white light by combining red, blue, and green LEDs. And yet, the green wavelength has been the most difficult to achieve.
Researchers originally discovered that green LEDs could be made by simply adding indium (In) to the gallium nitride (GaN) materials that composed blue LEDs, but the materials produced to date have been inefficient, resulting in green LEDs that are too dim to be used for lighting homes and offices. It is difficult to mix sufficient indium into the compound. Wetzel plans to focus instead on aspects of the “piezoelectric effect,” a property of some materials that causes them to produce an electrical field when pressure is applied. By using this effect, he hopes to develop a process to make higher-intensity and efficient green LEDs.
Interest in solid-state lighting is high because of its many advantages. LEDs are energy efficient, producing more energy per watt, and they last far longer than light bulbs. “Very much like a transistor, an LED would be a little piece of a semiconductor material with two wires sticking out,” says Wetzel. “You put it into place and for the next 10 to 20 years you don’t have to worry about it.”
See also: Closing the “Green Gap” in LEDs (Rensselaer Magazine)
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