When Woodall joined the research team at the Watson Center in 1962, he was part of an IBM initiative to replace mechanical data-processing equipment with smaller, more powerful electronic devices. Encouraged to pursue open-ended research, he and IBM colleague Hans Rupprecht began looking for materials that could convert electricity to light at room temperature without using a lot of power. Their success led to practical uses for laser beams, which had previously been produced only at very low temperatures in processes that used a great deal of power.
But Woodall says his first big break in the lab came when he, Rupprecht, and others found a new way to make a light-emitting diode. LED technology was then in its infancy; the first devices, which emitted infrared light, used too much power to be practical. Woodall perfected a process known as liquid-phase epitaxy to grow exceptionally pure crystals of gallium arsenide, the semiconductor from which infrared LEDs are made. His success made it possible for his team to fabricate an infrared LED that was efficient enough for widespread applications. Today, such LEDs are ubiquitous in TV remote controls.
“I never invented anything brand-new. My work is engineering new workable and efficient materials and devices,” says Woodall. “My middle name is ‘Mr. Fix-It.’ ”
Woodall and Rupprecht next began working on a way to produce an LED that would emit visible light. But to do that, they needed a better semiconductor. In 1957, Herbert Kroemer, then a researcher at RCA, had proposed layering different types of semiconductors, predicting that the interfaces between them would let researchers control the flow of current through the material so that they could tailor its electronic properties to specific purposes. Although that insight would earn Kroemer the Nobel Prize in 2000, it took Woodall’s exceptional crystal-growing skills to help bring the idea to life. In 1967, Woodall and his colleagues used liquid-phase epitaxy to grow another alloy, gallium aluminum arsenide, on a gallium arsenide substrate. The compound semiconductor based on the so-called lattice-matched GaAlAs/GaAs heterojunction could be used to produce diodes that emitted extremely bright red light. The material was incorporated into a flood of new electronic applications, including CD players and fiber-optic communication devices.
By 1972, the space race was well under way, and the pressure was on to develop efficient solar cells to generate electricity for orbiting spacecraft and satellites. Woodall realized that a compound semiconductor that turned electricity to light could also turn light to electricity. He and Harold Hovel used their new heterojunction to develop a high-efficiency solar cell that could withstand the rigors of space. Woodall and colleagues would also employ the material in a transistor that is widely used today in satellite communication systems and cell phones.