Tomorrow's light-emitting diodes will be made from smaller, cheaper and more-efficient zinc oxide materials rather than the exotic mixes of gallium, arsenide, indium and nitride used today. That's the vision of electrical engineers at the University of California, San Diego, who recently announced the world's first p-type zinc oxide nanowires.
"N-type zinc oxide nanowires are easy to make," said the researchers' leader, Deli Wang, "but it took my group over a year of concentrated effort to create the world's first p-type nanowires." Doctoral candidate Bin Xiang worked "day and night" to accomplish the task, said Wang, an EE professor at UCSD. Wang also had help on the project from EEs at Peking University (Beijing) as well as UCSD.
LEDs work by recombining electrons and holes, releasing the energy that separated them as a photon. Usually the electrons are supplied from an n-type semiconductor, from one side, with the holes supplied from the other side of the LED from a p-type semiconductor, using various formulations of exotic materials.
Until now, zinc oxide has been widely used as an n-type piezoelectric material, which can be fabricated into films or nanowires. But only a few labs have been able to formulate a p-type film from zinc oxide, and none had successfully formulated a p-type nanowire.
Wang's group created a p-type nanowire by carefully doping zinc oxide nanowires with phosphorus using standard chemical-vapor deposition techniques. The result is a source of holes, which holds the possibility of being juxtaposed with an n-type zinc-oxide nanowire to create a smaller, cheaper and more highly efficient LED.
For the future, Wang's group hopes to fabricate the world's first zinc oxide LED based on its nanowires.