Tuesday, March 20 , 2018, 4:48 am | Mostly Cloudy 51º


UCSB Researchers Shed Light on the Limits of LEDs

The team says they've found the cause of a drop in performance and efficiency

Researchers at UCSB say they’ve figured out the cause of a problem that has made light-emitting diodes (LEDs) impractical for general lighting purposes. Their work will help engineers develop a new generation of high-performance, energy-efficient lighting that could replace incandescent and fluorescent bulbs.

“Identifying the root cause of the problem is an indispensable first step toward devising solutions,” said Chris Van de Walle, a professor in the Materials Department at UCSB who heads the research group that carried out the work.

Van de Walle and his colleagues are working to improve the performance of nitride-based LEDs, which are efficient, nontoxic and long-lasting light sources. They investigated a phenomenon referred to as “droop,” the drop in efficiency that occurs in these LEDs when they’re operating at the high powers required to illuminate a room. The cause of this decline has been the subject of considerable debate, but the UCSB researchers say they’ve figured out the mechanism responsible for the effect by performing quantum-mechanical calculations.

LED droop, they conclude, can be attributed to Auger recombination, a process that occurs in semiconductors, in which three charge-carriers interact without giving off light. The researchers also discovered that indirect Auger effects, which involve a scattering mechanism, are significant — a finding that accounts for the discrepancy between the observed degree of droop and that predicted by other theoretical studies, which only accounted for direct Auger processes.

In nitride LEDs, ‘these indirect processes form the dominant contribution to the Auger recombination rate,” said Emmanouil Kioupakis, a postdoctoral researcher at UCSB and lead author of a paper published online April 19 in Applied Physics Letters. The other authors are Van de Walle, Patrick Rinke, now with the Fritz Haber Institute in Germany, and Kris Delaney, a project scientist at UCSB.

LED droop can’t be eliminated because Auger effects are intrinsic, but it could be minimized, the researchers say, by using thicker quantum wells in LEDs or growing devices along non-polar or semi-polar growth directions in order to keep carrier density low.

“With Auger recombination now established as the culprit, we can focus on creative approaches to suppress or circumvent this loss mechanism,” Van de Walle said.

The work was supported by the Center for Energy Efficient Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, and by UCSB’s Solid State Lighting and Display Center.

Computational resources were provided by the U.S. Department of Energy’s National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory, the California NanoSystems Institute’s computing facility at UCSB and the National Science Foundation-funded TeraGrid.

— Anna Davison represents the UCSB College of Engineering.

  • Ask
  • Vote
  • Investigate
  • Answer

Noozhawk Asks: What’s Your Question?

Welcome to Noozhawk Asks, a new feature in which you ask the questions, you help decide what Noozhawk investigates, and you work with us to find the answers.

Here’s how it works: You share your questions with us in the nearby box. In some cases, we may work with you to find the answers. In others, we may ask you to vote on your top choices to help us narrow the scope. And we’ll be regularly asking you for your feedback on a specific issue or topic.

We also expect to work together with the reader who asked the winning questions to find the answer together. Noozhawk’s objective is to come at questions from a place of curiosity and openness, and we believe a transparent collaboration is the key to achieve it.

The results of our investigation will be published here in this Noozhawk Asks section. Once or twice a month, we plan to do a review of what was asked and answered.

Thanks for asking!

Click here to get started >

Support Noozhawk Today

You are an important ally in our mission to deliver clear, objective, high-quality professional news reporting for Santa Barbara, Goleta and the rest of Santa Barbara County. Join the Hawks Club today to help keep Noozhawk soaring.

We offer four membership levels: $5 a month, $10 a month, $25 a month or $1 a week. Payments can be made through PayPal below, or click here for information on recurring credit-card payments.

Thank you for your vital support.

Reader Comments

Noozhawk is no longer accepting reader comments on our articles. Click here for the announcement. Readers are instead invited to submit letters to the editor by emailing them to [email protected]. Please provide your full name and community, as well as contact information for verification purposes only.

Daily Noozhawk

Subscribe to Noozhawk's A.M. Report, our free e-Bulletin sent out every day at 4:15 a.m. with Noozhawk's top stories, hand-picked by the editors.

Sign Up Now >

Meet Your Realtor Sponsored by Village Properties

Cimme Eordanidis
"Since I truly enjoy doing what I do, interacting with people and representing them during one of life's most exciting events is very rewarding."

Full Profile >