Monday, June 18 , 2018, 10:59 am | Fair 63º

 
 
 
 

UCSB Researchers Identify LED Diode Defects

Chris Van de Walle

Using state-of-the-art theoretical methods, UC Santa Barbara researchers have identified a specific type of defect in the atomic structure of a light-emitting diode (LED) that results in less efficient performance.

The characterization of these point defects could result in the fabrication of even more efficient, longer lasting 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 materials professor Chris Van de Walle, whose research group carried out the work.

In the world of high-efficiency solid-state lighting, not all LEDs are alike. As the technology is utilized in a more diverse array of applications — including search and rescue, water purification and safety illumination, in addition to their many residential, industrial and decorative uses — reliability and efficiency are top priorities.

Performance, in turn, is heavily reliant on the quality of the semiconductor material at the atomic level.

“In an LED, electrons are injected from one side, holes from the other,” explained Van de Walle. As they travel across the crystal lattice of the semiconductor — in this case gallium-nitride-based material — the meeting of electrons and holes (the absence of electrons) is what is responsible for the light that is emitted by the diode: As electron meets hole, it transitions to a lower state of energy, releasing a photon along the way.

Occasionally, however, the charge carriers meet and do not emit light, resulting in the so-called Shockley-Read-Hall (SRH) recombination. According to the researchers, the charge carriers are captured at defects in the lattice where they combine, but without emitting light.

The defects identified involve complexes 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,” explained lead author Cyrus Dreyer, who performed many of the calculations on the paper.

“It was the combination of the intuition that we have developed over many years of studying point defects with these new theoretical capabilities that enabled this breakthrough,” said Van de Walle, who credits co-author Audrius Alkauskas with the development of a theoretical formalism necessary to calculate the rate at which defects capture electrons and holes.

The method lends itself to future work identifying other defects and mechanisms by which SRH recombination occurs, said Van de Walle.

“These gallium vacancy complexes are surely not the only defects that are detrimental,” he said. “Now that we have the methodology in place, we are actively investigating other potential defects to assess their impact on non-radiative recombination.”

The paper has been published as a featured article in the April 4 issue of Applied Physics Letters [APL 108, 141101 (2016)], with an accompanying figure on the cover of the journal.

This work was funded by U. S. Department of Energy Office of Science and by Marie Skłodowska-Curie action of the European Union.

Sonia Fernandez writes for the UCSB Office of Public Affairs and Communications.

 

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.

Become a Noozhawk Supporter

First name
Last name
Enter your email
Select your membership level
×

Payment Information

You are purchasing:

Payment Method

Pay by Credit Card:

Mastercard, Visa, American Express, Discover

Pay with Apple Pay or Google Pay:

Noozhawk partners with Stripe to provide secure invoicing and payments processing.

  • 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 >

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 >