Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Rensselaer Researchers Identify Cause of LED “Efficiency Droop”

31.07.2013
Rensselaer Polytechnic Institute researchers have identified the mechanism behind a plague of LED light bulbs: a flaw called “efficiency droop” that causes LEDs to lose up to 20 percent of their efficiency as they are subjected to greater electrical currents.

Efficiency droop, first reported in 1999, has been a key obstacle in the development of LED lighting for situations, like household lighting, that call for economical sources of versatile and bright light.

In a paper recently published in Applied Physics Letters, the researchers identify a phenomena known as “electron leakage” as the culprit. The research offers the first comprehensive model for the mechanism behind efficiency droop, and may lead to new technologies to solve the problem, said E. Fred Schubert, the Wellfleet Senior Constellation Professor of Future Chips at Rensselaer, founding director of the university’s National Science Foundation-funded Smart Lighting Engineering Research Center, and senior author on the study.

“In the past, researchers and LED manufacturers have made progress in reducing efficiency droop, but some of the progress was made without understanding what causes the droop,” said Schubert. “I think now we have a better understanding of what causes the droop and this opens up specific strategies to address it.”

Light-emitting diodes take advantage of the fact that high-energy electrons emit photons, i.e. particles of light, as they move from a higher to a lower energy level. The light-emitting diode is constructed of three sections: an “n-type” section of crystal that is loaded with negatively charged electrons; a p-type section of crystal that contains many positively charged “holes;” and a section in between the two called the “quantum well” or “active region.”

David Meyaard, first author on the study and a doctoral student in electrical engineering, explains that electrons are injected into the active region from the n-type material as holes are injected into the active region from the p-type material. The electrons and holes move in opposite directions and, if they meet in the active region, they recombine, at which point the electron moves to a lower state of energy and emits a photon of light. Unfortunately, researchers have noticed that as more current is applied, LEDs lose efficiency, producing proportionally less light as the current is increased.

Meyaard said the team’s research shows that, under the “high current regime,” an electric field develops within the p-type region of the diode, allowing electrons to escape the active region where they would otherwise recombine with holes and emit photons of light. This phenomenon, known as “electron leakage,” was first proposed more than five years ago, but Meyaard said the team’s research is the first incontrovertible evidence that it is the cause behind efficiency droop. Meyaard said the team identified the electric field as it began to build up, and showed that, after a sufficiently strong field is built up, the electrons escape out of the active region.

“We measure excellent correlation between the onset of field-buildup and the onset of droop,” said Meyaard. “This is clear evidence that the mechanism is electron leakage, and we can describe it quantitatively. For example, in one key result reported in the paper, we show the onset of high injection and the onset of droop and you can see that they are very nicely correlated. And that was just not possible in the past because there was really no theoretical model that described how electron leakage really works.”

Schubert said their work shows that because electrons have a greater “mobility” than holes, the diode is made from disparate types of carriers.

“If the holes and the electrons had similar properties, there is a symmetry; both would meet in the middle, where the quantum well is, and there they recombine,” said Schubert. “What we have instead is a material system where the electrons are much more mobile than the holes. And because they are very mobile, they diffuse more easily, they also react more easily to an electric field. Because of that asymmetry, or disparity, we have a propensity of the electrons to ‘shoot over’ and to be extracted from the quantum well. And so they don’t meet the hole in the active region and so they don’t emit light.”

Meyaard and Schubert said the team has now turned their attention to developing a new structure for LEDs, based on the model, which they look forward to introducing.

The paper, published in the June 27 edition of Applied Physics Letters, is titled “Identifying the cause of the efficiency droop in GaInN light-emitting diodes by correlating the onset of high injection with the onset of the efficiency droop.”

Contact: Mary L. Martialay
Phone: (518) 276-2146
E-mail: martim12@rpi.edu

Mary Martialay | EurekAlert!
Further information:
http://www.rpi.edu

More articles from Physics and Astronomy:

nachricht NASA spacecraft investigate clues in radiation belts
28.03.2017 | NASA/Goddard Space Flight Center

nachricht Researchers create artificial materials atom-by-atom
28.03.2017 | Aalto University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Transport of molecular motors into cilia

28.03.2017 | Life Sciences

A novel hybrid UAV that may change the way people operate drones

28.03.2017 | Information Technology

NASA spacecraft investigate clues in radiation belts

28.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>