Examination of Single Perovskite Crystals Reveals Much Untapped Potential for Solar and LEDs
LIGHTimes News Staff
February 3, 2015...Engineers at the University of Toronto have for the first time demonstrated
some of the optoelectronic properties of pure perovskite crystals. This
emerging family of solar-absorbing materials and understanding their
optoelectronic properties could lead to more efficient and cheaper solar panels
and LEDs. Through their examination of the properties of single perovskite
materials, the researchers revealed that perovskites still have much untapped
potential for use in solar panels and LEDs.
The perovskites, are particularly good at absorbing visible light, but they
had never before been thoroughly studied as perfect single crystals. The
researchers employed a new technique to grow pure perovskite crystals and then
studied electrons move through the material as light is converted to
Professor Ted Sargent of the University of Toronto's Edward S. Rogers Sr.
Department of Electrical & Computer Engineering and Professor Osman Bakr of
the King Abdullah University of Science and Technology (KAUST) used a
combination of laser-based techniques to measure certain properties of the
perovskite crystals. They tracked down the rapid motion of electrons in the
material. From this they were able to determine the diffusion length--how far
electrons can travel without imperfections in the material trapping them--as
well as mobility—how fast the electrons can move through the material.
This week, they published their work in the journal Science.
“Our work identifies the bar for the ultimate solar
energy-harvesting potential of perovskites,” said Riccardo Comin, a
post-doctoral fellow with the Sargent Group. “With these materials
it’s been a race to try to get record efficiencies, and our results
indicate that progress is slated to continue without slowing
Certified efficiencies of perovskites have reached new heights of just over
20 percent in recent years. Such efficiency starts to approach the performance
of the state-of-the-art commercial-grade silicon-based solar panels mounted in
deserts in spain and on roofs in California.
“In their efficiency, perovskites are closely approaching
conventional materials that have already been commercialized,” said
Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author of
the paper. “They have the potential to offer further progress on
reducing the cost of solar electricity in light of their convenient
manufacturability from a liquid chemical precursor.”
In solar panels, light hits the surface of the perovskite material and gets
absorbed, thereby exciting electrons. These electrons easily traverse the
crystal structure to electrical contacts on the underside, creating electric
current. In LEDs the process happens in reverse. The slab is first powered with
electricity, which injects electrons and then releases energy as light.
The Sargent Group is conducting parallel work that aims to improve the
performance of solar-absorbing particles called colloidal quantum dots.
“Perovskites are great visible-light harvesters, and quantum dots are
great for infrared,” said Professor Sargent. “The materials are
highly complementary in solar energy harvesting in view of the sun’s
broad visible and infrared power spectrum.”
“In future, we will explore the opportunities for stacking
together complementary absorbent materials,” said Dr. Comin.
“There are very promising prospects for combining perovskite work and
quantum dot work for further boosting the efficiency.”
Graphene and LEDs Made with Super-Thin Crystals Pave the Way for Flexible Electronics
LIGHTimes News Staff
February 3, 2015...Researchers from the University of Manchester and the University of
Shiefield have successfully created extremely flat LEDs with grapheme and 10 to
40 atom thick crystals. Nobel Laureate Sir Kostya Novoselov led the team that
engineered the LEDs on the atomic level. They published the results in the
Nature Materials. The unique properties of Graphene may someday allow
the creation of semi-transparent, flexible electronics, according to the
The new research demonstrated that graphene and related materials that are
essentially 2D could be employed in light emitting devices for the
next-generation of mobile phones, TVs, and tablets and televisions making them
incredibly thin, and even flexible, durable and semi-transparent. The
researchers combined different ultra-thin crystals that can emit light from
across their whole surfaces. Such LEDs may one day form flexible and
One-atom thick graphene was first isolated and explored in 2004 at The
University of Manchester. Other 2D materials, such as molybdenum disulphid and
boron nitiride have been discovered since then, opening new areas of research
and potential applications. Stacked layers of various "2D" materials, with the
addition of quantum wells to control the movement of electrons have now
revealed the potential for customized, grapheme-based optoelectronics.
Freddie Withers, the University of Manchester's Royal Academy of Engineering
Research Fellow, who led the devices' production said, “As our new
type of LED’s only consist of a few atomic layers of 2D materials they
are flexible and transparent. We envisage a new generation of optoelectronic
devices to stem from this work, from simple transparent lighting and lasers and
to more complex applications.”
Explaining the construction of the LED device, Sir Kostya Novoselov said,
“By preparing the heterostructures on elastic and transparent
substrates, we show that they can provide the basis for flexible and
“The range of functionalities for the demonstrated
heterostructures is expected to grow further on increasing the number of
available 2D crystals and improving their electronic quality.”
Professor Alexander Tartakovskii, from The University of Sheffield claimed,
“Despite the early days in the raw materials manufacture, the quantum
efficiency (photons emitted per electron injected) is already comparable to
2015 Draper Prize for Engineering Goes to LED Lighting Pioneers
LIGHTimes News Staff
January 8, 2015...The US National Academy of Engineering (NAE) has awarded the 2015 Charles
Stark Draper Prize for Engineering to Nick Holonyak Jr, Isamu Akasaki, M.
George Craford, Russell Dupuis, and Shuji Nakamura for “the invention,
development, and commercialization of materials and processes for LEDs. The
prize will be presented at a gala dinner in Washington D.C. on 24 February.
In 1988, in honor of the memory of Charles Stark Draper, known as the
'father of inertial navigation', the National Association of Engineering (NAE)
established the $500,000 annual Draper Prize at the request of Charles Stark
Draper Laboratory Inc.
The Draper Prize, which is NAE's highest honor, is given to engineers for
achievements that have significantly benefited society by improving the quality
of life, and/or expanding access to information.
“These prize-winning engineers were the pioneers in a technology
that has changed the world we live in, from the aesthetics in our homes, to
advancements in our visual capabilities, and to environmental
stewardship,” stated NAE president C D. Mote Jr.
In 1962, Nick Holonyak Jr created the first visible, red LED while working
at General Electric. He studied III-V materials including gallium arsenide
(GaAs) and found that adding phosphorus (P) to gallium arsenide resulted in a
shortened wavelength. He ultimately tuned the GaAsP LED to emit visible red
lightIn 1972, George Craford invented the first yellow LED and increased its
brightness by adding nitrogen to the GaAsP LED. Craford also participated in
developing processes for the first large-scale commercial production of red
LEDs. He later led work that resulted in the first high-brightness yellow and
red LEDs, available in 1992, and subsequently contributed to the development of
high-power white LEDs.
Russell Dupuis developed and refined the metal-organic chemical vapor
deposition (MOCVD) process in 1977, which enabled the production of
high-brightness LEDs and is now the basis of nearly all production of
high-brightness LEDs, and other high-speed optoelectronic devices including
laser diodes and solar cells.
In 1987 Isamu Akasaki used MOCVD to grow high-quality gallium nitride
crystals on sapphire substrates, creating the first blue LED (which later
enabled efficient, bright, white light sources).
In 1992, Shuji Nakamura also made important contributions to InGaN-based
high-brightness double-heterostructure blue LEDs, as well as laser diodes that
allowed development of the high-density digital video disk (Blu Ray DVD).
Nakamura, who is a professor of materials and of electrical & computer
engineering at University of California Santa Barbara (UCSB), received the 2014
Nobel Prize in Physics (shared with professors Isamu Akasaki and Hiroshi Amano)
for helping develop the first high-brightness blue LED.
British Reseachers Create Simulations that More Accurately Predict Properties of GaN
LIGHTimes News Staff
January 8, 2015...Researchers from University College London (UCL) worked with teams at
Daresbury Laboratory and the University of Bath to reveal the complex
properties of gallium nitride using computer simulations. Accurate predictions
of these properties can help make better blue LEDs and predict their output
before actual fabrication.
LEDs employ two layers of semiconductors: a conduction layer with electrons
available and a layer with positive charges or holes. When an electron and a
hole meet, they emit a photon (light particle). A cristalline film of a
particular material--GaN for blue LEDs--is grown and then doped. Dopants donate
an extra positive or negative charge to the material.
GaN, the key material for blue LEDs, has a large energy gap between
electrons and holes (known as a wide bandgap). The wide bandgap is essential
for tuning the emitted photons to produce blue light. Doping to donate mobile
negative charges in the material proved to be easy. However, donating positive
charges from GaN failed completely. The innovation, which won the inventors of
the blue LED the Nobel Prize for physics last year, required doping GaN with
unexpectedly large amounts of magnesium.
"While blue LEDs have now been manufactured for over a decade,"
said John Buckeridge (UCL Chemistry), the study's lead author, "there has
always been a gap in our understanding of how they actually work, and this is
where our study comes in. Based on what is seen in other semiconductors such as
silicon, you would expect each magnesium atom added to the crystal to donate
one hole. But in fact, to donate a single mobile hole in GaN, at least a
hundred atoms of magnesium have to be added. It's technically extremely
difficult to manufacture GaN crystals with so much magnesium in them, not to
mention that it's been frustrating for scientists not to understand what the
The team published details of their findings in the journal Physical Review
Letters. The team used highly sophisticated computer simulations to accurately
predict the unusual behavior of doped GaN at the atomic level. While a quantum
mechanical model can make accurate predictions about perfect crystals with
repeating patterns of atoms, such a model has difficulty dealing with defects
which do not fit the repeating pattern of atoms. The computer simulations for
accurate prediction of GaN crystals with some defects requires use of
supercomputers because of the large numbers of atoms and their interactions.
"To make an accurate simulation of a defect in a semiconductor such as
an impurity, we need the accuracy you get from a quantum mechanical
model," said David Scanlon (UCL Chemistry), a co-author of the article.
"Such models have been widely applied to the study of perfect crystals,
where a small group of atoms form a repeating pattern. Introducing a defect
that breaks the pattern presents a conundrum, which required the UK's largest
supercomputer to solve. Indeed, calculations on very large numbers of atoms
were therefore necessary but would be prohibitively expensive to treat the
system on a purely quantum-mechanical level."
The team solved the the issue with an approach pioneered in another Nobel
Prize winning research: hybrid quantum and molecular modeling, the subject of
2013's Nobel prize in Chemistry. The new models simulate different parts of a
complex chemical system with different levels of theory. Some previously
unexplained experimental results about the behavior of GaN now fit with the new
Richard Catlow (UCL Chemistry), one of the study's co-authors said, "Our
simulation shows that the behavior of the semiconductor is much more complex
than previously imagined, and finally explains why we need so much magnesium to
make blue LEDs successfully."
"The simulation tells us that when you add a magnesium atom, it replaces
a gallium atom but does not donate the positive charge to the material, instead
keeping it to itself," Catlow said. "In fact, to provide enough energy
to release the charge will require heating the material beyond its melting
point. Even if it were released, it would knock an atom of nitrogen out of the
crystal, and get trapped anyway in the resulting vacancy."
"In fact, to provide enough energy to release the charge will require
heating the material beyond its melting point. Even if it were released, it
would knock an atom of nitrogen out of the crystal, and get trapped anyway in
the resulting vacancy," Catlow added.
Aron Walsh of Bath Chemistry noted, that the team is looking forward to
using the new simulations to investigate the properties of heavily defective
GaN and help develop alternative doping strategies to improve the efficiency of
Startup Allos Semiconductors now Offers Licensing for Azzurro's GaN-on-Si Patents and Technology
LIGHTimes News Staff
December 16, 2014...ALLOS Semiconductors GmbH, a newly founded company based in Dresden,
Germany, who specializes in GaN-on-Si technology, announced that it has
acquired all the patents and technology of former Azzurro Semiconductors at an
auction. In addition to its existing offering of GaN-on-Si technology ALLOS is
now making the AZZURRO technology platform available through technology
transfer, licencing and customised development work.
In June of 2014, ALLOS Semiconductors was formed to help meet the growing
demand for technology of growing gallium nitride on silicon substrates
(GaN-on-Si). An increasing number of LED and power semiconductor companies want
to be able to grow 150 and 200 mm GaN-on-Si wafers to supply cost-effective
high-quality GaN devices that can be processed in standard silicon fabs.
Allos complements the GaN-on-Si technology licensing with advice on business
and technology strategies and support for setting up GaN-on-Si operations all
the way from establishing a epitaxial wafer fab to market entry.
Cubic GaN Shows Potential for LEDs
LIGHTimes News Staff
December 16, 2014...Anvil Semiconductors and the Cambridge Centre for GaN at the University of
Cambridge report having grown cubic GaN on 3C-SiC (silicon carbide) wafers using
MOCVD. Anvil produced the underlying 3C-SiC layers using the company's patented
stress relief IP that enables growth of device quality silicon carbide on 100mm
diameter silicon wafers. Anvil contends that the process can work with 150mm
diameter wafers and possibly beyond without modification and is therefore
suitable for industrial-scale applications. In a project funded by Innovate UK,
the MOCVD growth trials at Cambridge resulted in single phase, cubic GaN. The
layers, characterized by XRD, TEM, photoluminescence and AFM, have potential
for LED applications.
According to the researchers, the cubic GaN may be able to remove the strong
internal electric fields, which plague conventional green LEDs, impair
recombination, and make it difficult to address high internal quantum
efficiency (IQE). Also, the researchers note that cubic GaN has a narrower
bandgap and improved p-type electrical properties compared to the conventional
hexagonal GaN phase used for LEDs. Therefore, a commercializable process to
produce cubic GaN on large diameter silicon wafers may help increase the
efficiency and reduce the cost of LED lighting.
The team plans to continue development to eventually fabricate sample LEDs
before looking for an industry partner to commercialize the technology.
Sanan Orders 50 MOCVD Reators from Veeco for LED Production
LIGHTimes News Staff
December 12, 2014...Veeco Instruments Inc. of Plainview, New York USA, announced that Sanan
Optoelectronics, the largest LED manufacturer in China, has ordered 50
TurboDisc® EPIK700™ Gallium Nitride (GaN) Metal Organic Chemical Vapor
Deposition (MOCVD) reactors for the production of LEDs. This order is the
equivalent of 25 EPIK700 MOCVD “C2” (cluster) systems.
“Sanan chose the EPIK700 due to its industry leading cost of
ownership model and excellent footprint efficiency,” said Zhiqiang
Lin, vice chairman and CEO of Sanan. “Our beta testing of EPIK700
proved its production-worthiness, and we are confident in its capabilities and
value to our Xiamen business expansion plans. Veeco has been a great partner
for Sanan as we have solidified our position as the top LED manufacturer in
China and increased our business outside of China as well.”
Veeco's EPIK700 MOCVD system uses the company's TurboDisc technology to
achieve a cost per wafer savings of up to 20 percent compared to previous
generation MOCVD systems. The savings comes through increased productivity,
improved wafer uniformity, and reduced operating expenses.
“This large order from Sanan, the largest single purchase order
Veeco has received since 2009, speaks volumes about the EPIK700’s
production readiness and the recovery in the MOCVD market,” said
John Peeler, Veeco’s chairman and CEO. “We are in a great
position to continue to serve our LED customers with the best MOCVD technology
and customer support, and remain the industry leader.”
EV Group Establishes Nanoimprint Lithography Competence Center
LIGHTimes News Staff
December 4, 2014...EV Group (EVG) based in St. Florian, Austria, a supplier of wafer bonding
and lithography equipment, announced that it has established the
NILPhotonics(TM) Competence Center. The NILPhotonics(TM) Competence Center
assists customers in leveraging EVG's suite of nanoimprint lithography (NIL)
solutions for new and enhance photonics products and applications including
LEDs and photovoltaic (PV) cells.
EVG says that in LEDs NIL-enabled photonic structures can improve light
extraction, and in PV cells NIL-enabled photonic structures can improve light
capturing. Additionally, NIL-enabled photonic structures in laser diodes enable
device characteristic tailoring and optimization to improve performance. The
Competence Center includes dedicated, global process teams, pilot-line
production facilities and services at its cleanrooms at EVG's headquarters in
Austria and its subsidiaries in Japan and North America.
EVG says that the new NILPhotonics Competence Center builds on the company's
more than 15 years of NIL experience and what the company claims to be the
largest installed base of NIL systems worldwide. EVG's NIL equipment portfolio
includes the recently introduced EVG7200 UV-NIL system, which supports EVG's
next-generation SmartNIL(TM) large-area soft NIL process for high-volume
manufacturing. The company boasts that the EVG7200 with SmartNIL provides
unmatched throughput and cost-of-ownership advantages over competing NIL
"Nanoimprint lithography is an enabling technology for the design and
manufacture of all kinds of photonic structures, which can significantly
shorten time to market and lower cost of production compared to conventional
technologies, such as electron-beam writing and stepper systems for optical
lithography," stated Markus Wimplinger, corporate technology development
and IP director at EV Group.
"For example, compared with conventional lithography, our full-wafer
nanoimprinting technology can pattern true three-dimensional structures in the
sub-micron to nano-range as well as features as small as 20 nm, which opens up
a range of new photonic applications.
With our NILPhotonics Competence Center, we're not just providing our
customers with the most advanced NIL systems; we're also working closely with
them during product development to help them determine how best to optimize
their product designs and processes to take advantage of the resolution and
cost-of-ownership benefits that NIL brings."
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