A team of University of California (UC), Santa Barbara researchers has pinpointed a unique defect in the atomic structure of a light-emitting diode (LED) that decreases performance, a finding that could help scientists locate these defects in current LEDs and develop more durable and efficient LED lighting.
"Techniques are available to assess whether such defects are present in the LED materials and they can be used to improve the quality of the material," said Chris Van de Walle, a UC materials professor who oversaw the research.
The LEDs used in solid-state lighting technology are not identical, and their use in various applications - such as water purification and safety illumination - makes reliability and efficiency a top priority during their development. One of the biggest things that affects these two performance characteristics is the quality of the atomic semiconductor material.
"In an LED, electrons are injected from one side, holes from the other," Van de Walle said.
Electrons make their way across the LED semiconductor's gallium nitride-based material, and when they meet the hole that lacks electrons, they shift to a lower state of energy, releasing a photon and stimulating the emission of light from the diode.
However, sometimes this process does not occur, causing a Shockley-Read-Hall (SRH) recombination, something that happens when the electrons are caught in defects in the lattice, preventing the emission of light. These defects are a combination of gallium vacancies with oxygen and hydrogen.
"These defects had been previously observed in nitride semiconductors, but until now, their detrimental effects were not understood," said Cyrus Dreyer, a UC scientist and lead author of the paper.
The discovery of this unique defect in LED diodes can help scientists create more efficient solid-state lighting in the future.
"These gallium vacancy complexes are surely not the only defects that are detrimental," Van de Walle said. "Now that we have the methodology in place, we are actively investigating other potential defects to assess their impact on nonradiative recombination."
The findings were published in the April 4 issue of Applied Physics Letters.
