Subscribe to our free daily newsletters
. 24/7 Space News .




Subscribe to our free daily newsletters



TECH SPACE
Trace metal recombination centers kill LED efficiency
by Staff Writers
Santa Barbara CA (SPX) Nov 08, 2016


This is a schematic illustration of Shockley-Read-Hall (SRH) recombination due to iron in GaN. Iron is a deep acceptor with a defect level (black line) close to the GaN conduction band (green). The charge density corresponding to this localized level is illustrated in the middle of the figure. Conventional SRH recombination (left) would proceed via electron capture from the conduction band into the defect level, but the overall rate would be limited by slow capture of holes because the defect level is far from the valence band (blue). The presence of excited states enhances the hole capture rate (right) such that the overall SRH recombination process becomes very efficient. Image courtesy Sonia Fernandez. For a larger version of this image please go here.

Using cutting-edge first-principles calculations, researchers at the University of California, Santa Barbara (UCSB) have demonstrated the mechanism by which transition metal impurities - iron in particular - can act as nonradiative recombination centers in nitride semiconductors. The work highlights that such impurities can have a detrimental impact on the efficiency of light-emitting diodes (LEDs) based on gallium nitride or indium gallium nitride.

For LEDs, high-purity material is essential to lighting technology, such as residential and commercial solid-state lighting, adaptive lighting for automobiles, and displays for mobile devices. Imperfections at the atomic scale can limit the performance of LEDs through a process known as Shockley-Read-Hall recombination. The operation of an LED relies on the radiative recombination of electrons and holes, which results in the emission of photons. Defects or impurities can act as a source of nonradiative recombination and prevent the emission of light, lowering the LED efficiency.

The UCSB researchers, in collaboration with researchers from Rutgers University, the University of Vienna, the KTH Royal Institute of Technology in Sweden and the Center for Physical Sciences and Technology in Lithuania, have identified that iron, even at concentrations less than parts-per-million, can be highly detrimental.

Transition metal impurities such as iron have long been known to severely impact devices based on traditional semiconductors such as silicon and gallium arsenide, leading these impurities to be referred to as "killer centers." It is therefore surprising that little attention has been devoted to understanding the role of transition metals in recombination dynamics in GaN.

"A naive application of Shockley-Read-Hall theory, based on an inspection of defect levels within the band gap, would lead one to conclude that iron in GaN would be harmless," explained Dr. Darshana Wickramaratne, lead author on the paper. "However, our work shows that excited states of the impurity play a key role in turning it into a killer center."

The UCSB scientists identified a recombination pathway by which iron can lead to severe efficiency loss. Sophisticated first-principles calculations were essential to identify and understand the role of the excited states in the recombination process.

"Taking these excited states into account completely changes the picture," emphasized Dr. Audrius Alkauskas, another member of the research team. "We strongly suspect that such excited states play a key role in other recombination phenomena, opening up new avenues for research."

The results highlight that strict control over growth and processing is required to prevent the unintentional introduction of transition metal impurities. Sources of iron contamination include the stainless steel reactors that are used in some growth techniques for nitride semiconductors.

"Increasing the efficiency of light emission is a key goal for the solid-state lighting industry," said UCSB Materials Professor Chris Van de Walle, who led the research team. "Our work focuses attention on the detrimental impact of transition metals and the importance of suppressing their incorporation."

The work has been published in the October 17 issue of Applied Physics Letters [Appl. Phys. Lett. 109, 162107 (2016)], and was funded by the U. S. Department of Energy (DOE), Office of Science, and by Marie Sklodowska-Curie Action of the European Union.


Comment on this article using your Disqus, Facebook, Google or Twitter login.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only

.


Related Links
University of California - Santa Barbara
Space Technology News - Applications and Research






Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
TECH SPACE
Lehigh scientists fabricate a new class of crystalline solid
Bethlehem PA (SPX) Nov 08, 2016
Scientists at Lehigh University, in collaboration with Lawrence Berkeley National Laboratory, have demonstrated the fabrication of what they call a new class of crystalline solid by using a laser heating technique that induces atoms to organize into a rotating lattice without affecting the macroscopic shape of the solid. By controlling the rotation of the crystalline lattice, the researche ... read more


TECH SPACE
Progress, but uphill slog for women in tech

NavCube could support an X-ray communication test in space

NASA, Navy practice Orion module recovery

Weightless tourism just 4 years away

TECH SPACE
JCSAT-15 arrives in Kourou for Dec Ariane 5 launch

Aerojet Rocketdyne completes CST launch abort engine hot fire tests

China launches first heavy-lift rocket

NASA Uses Tunnel Approach to Study How Heat Affects SLS Rocket

TECH SPACE
Mars' ionosphere shaped by crustal magnetic fields

Iron-Loving Bacteria A Model For Mars Life

Opportunity makes small U-turn to reach summit of Spirit Mound

'Millions' needed to continue Europe's Mars mission: ESA chief

TECH SPACE
Long March-5 reflects China's "greatest advancement" yet in rockets

New heavy-lift carrier rocket boosts China's space dream

Long March-7 being assembled, to transport Tianzhou-1

Kuaizhou-1 scheduled to launch in December

TECH SPACE
AsiaSat wins patent for effective satellite broadband connectivity to aircraft

Sun-observing MinXSS CubeSat to yield insights into solar flare energetics

Optus achieves full certification of 4 teleports

ISRO's World record bid: Launching 83 satellites on single rocket

TECH SPACE
We gather here today to join lasers and anti-lasers

Trace metal recombination centers kill LED efficiency

Studying structure to understand function within 'material families'

Study: Math scares everyone, even physicists

TECH SPACE
What happens to a pathogenic fungus grown in space?

How Planets Like Jupiter Form

Giant Rings Around Exoplanet Turn in the Wrong Direction

Preferentially Earth-sized Planets with Lots of Water

TECH SPACE
Mystery solved behind birth of Saturn's rings

Last Bits of 2015 Pluto Flyby Data Received on Earth

Uranus may have two undiscovered moons

Possible Clouds on Pluto, Next Target is Reddish




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News






The content herein, unless otherwise known to be public domain, are Copyright 1995-2017 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement