You might not know what "lattice-matched heterojunctions" are, but if you stopped at a new stoplight, played a DVD or used a laser pointer, you've made use of technology pioneered by Jerry Woodall, distinguished professor of electrical and computer engineering at the University of California, Davis. Woodall's work, begun in the 1960s at IBM Research, is the basis for cheap, energy-efficient light-emitting diodes, or LEDs, and lasers.
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| Electrical and computer engineer Jerry Woodall, newly elected to the National Academy of Inventors, measures the responsiveness of an experimental solar cell. (Gregory Urquiaga/UC Davis photo) |
Woodall, who has published more than 350 papers and 85 patents, has received wide recognition including receiving the National Medal of Technology and Innovation from President George W. Bush in 2001. This December, Woodall adds another honor with election to the National Academy of Inventors.
This year's new fellows will be formally inducted into the National Academy of Inventors March 7 by Margaret Focarino, U.S. commissioner for patents, during a ceremony at the United States Patent and Trademark Office Headquarters in Alexandria, Va.
But Woodall isn't done with inventing. He is now venturing into two of engineering's "grand challenges," in energy and water — two areas in which UC Davis excels — using discoveries he made on the way to creating high-efficiency infra-red and red LEDs.
When Woodall started his career at IBM Research in 1962, his employer was looking for another transistor: amplifiers, rather than light-emitting devices.
Woodall found ways to make junctions between two different semiconductors so that the combined device would emit light efficiently. The difference in "bandgap energy" between the two materials determines the wavelength of emitted light particles. Others had made inefficient red or low brightness LEDs based on combinations of the semiconductors gallium arsenide and gallium phosphide, but Woodall found the right combination of gallium arsenide and aluminum arsenide to make the first bright, efficient red LED that was commercially viable.
Some of us remember the red glowing displays of the first digital calculators and digital watches. The technology also made remote controls, which use infrared LEDs, feasible. And they enabled development of cheap lasers, which opened the way for everything from laser pointers and optical fiber communications to DVD players and other storage devices.
"I didn't invent the continuous wave injection laser, but I enabled it," Woodall said.
In the 1990s, other researchers, building on Woodall’s heterojunction work, developed blue LEDs and lasers, which made possible the high information density of high-definition (Blu-Ray) DVDs. White LEDs, which use a phosphor screen to generate bright white light, are rapidly becoming popular for energy-efficient lighting.
"It's all based on the heterojunction," Woodall said. "That's why I got to shake the president's hand."
Woodall left IBM in 1993 and worked at Purdue and Yale universities before coming to UC Davis in 2012. At this stage of his career, he's turning to two new challenges for the world: energy and water. That's a good match with UC Davis, with its depth of creative expertise from engineering to policy in both fields.
"There's a lot more that can be done with lasers and LEDs, but it's not what you'd call a "grand challenge," Woodall said. "But water is."
"I know how to make potable water remotely, generate energy and clean water and modernize a remote village," he said.
The key is the most effective energy storage material available on Earth: aluminum.
Wait, aluminum? Isn't that a light, silvery metal for making pots and boats and aircraft parts?
Aluminum, in fact, is the third most abundant element on Earth. It does not exist naturally as a metal, because it combines with oxygen to form aluminum oxides. In fact, aluminum loves oxygen so much that if you could extract the heat involved in combining the two, you would get 8.8 kilowatt-hours per kilogram of metal. That makes aluminum a better energy store than coal.
Futurists have long looked to hydrogen as the clean future fuel to replace carbon-based fuels like coal, oil and natural gas. But while hydrogen can carry a lot of energy by weight, its density is very low — you need an enormous volume to carry a significant amount of energy, or you need to store compressed hydrogen under high pressure.
"The energy density of hydrogen is good by mass but terrible by volume," Woodall said. Aluminum, on the other hand, "can't be beat" for energy storage by volume, he said.
Leave metallic aluminum exposed to air, and it will quickly form a skin of aluminum oxide. The secret to Woodall's process is to find a way to oxidize aluminum while capturing heat and hydrogen. And that discovery goes back to Woodall's early work on semiconductors.
In 1968, Woodall was trying to grow crystals in mixtures of aluminum dissolved in liquid gallium. He discovered that when water was added to the mixture, the aluminum split the water, releasing hydrogen gas and heat and forming aluminum oxides.
Since then, he's worked to refine the process, use less gallium and make it more efficient and controllable.
Aluminum metal is made by using electricity to melt bauxite ore in a salt solution. Woodall envisages using a solar power plant, or wind farm, to power an aluminum smelter and make aluminum metal — a compact, stable energy store. This aluminum could be used to fuel one of his reactors, generating hydrogen that runs a fuel cell that makes electricity and heat. The fuel cell also regenerates clean water, and both the gallium and the aluminum can be recycled and used again.
Woodall recently started a company, Hydroalumina, to develop and sell reactors based on the "Woodall process" that can make high-purity hydrogen or alumina.
In other projects, Woodall's lab is working on a new type of solar cell that captures energy from both light and heat, and continues to work on a truly green LED.
Over the past 50 years, Woodall's work has made possible generations of new devices that have changed our lives but that rapidly get replaced by new gadgets. In contrast, Woodall, who describes himself as a "fairly good pianist," keeps a Steinway at home that "will never wear out," he says. In July this year, he volunteered to play for a music appreciation class held in the Mondavi Center's Jackson Hall.
"To play in a real concert hall, that fulfilled a bucket list item for me," he said. "Better than shaking hands with the president."
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