Oxford Instruments Launches PlasmaPro100 Sapphire Single-wafer Etch
LIGHTimes News Staff
June 20, 2013...Oxford Instruments Plasma Technology has introduced the PlasmaPro100
Sapphire for etching HBLED materials. The company claims that it minimizes cost
of ownership and maximizes yield. The system has Electrostatic Clamp technology
which can clamp sapphire. The system can effectively etch GaN on sapphire and
silicon. It has a high power ICP source producing a high density plasma;
magnetic spacer for enhanced ion control; and a high conductance pumping system
delivering maximum gas throughput at low pressures. The company boasts of the
new systems reliability, uptime and ease of serviceability.
Michelle Bourke, production business group director at Oxford Instruments
commented, “The PlasmaPro100 Sapphire is designed specifically to
address the harsh chemistries required forHBLED materials, delivering
fast etch rates uniformly on wafers up to 200mm in diameter. At Oxford
Instruments we strive to provide the most innovative, cost effective and
reliable process solutions for our customers. This latest system is designed to
encompass all these requirements.”
According to Oxford Instruments, the PlasmaPro100 Sapphire’s
technology promises manufacturers the tools to deliver more efficient, lower
cost lighting that is needed worldwide to assist this lighting revolution.
Hong Kong University Researchers Create First Yellow LEDs from Nitride Semiconductor MQWs on Silicon
LIGHTimes News Staff
June 18, 2013...Hong Kong University of Science and Technology (HKUST) has developed silicon
substrate growth of high-performance green and yellow nitride semiconductor
LEDs. Details of the development were published in the May 29th issue of IEEE
Electronic Device Letters. The researchers claim their 565nm yellow LEDs
are the first multi-quantum well (MQW) devices produced on silicon.
In theory, using silicon as a substrate would lower material cost and enable
economies of scale in mass production from the larger wafer diameters. However,
the quality of nitride semiconductors on silicon suffer from the larger lattice
mismatch compared with conventional, more expensive substrates of free-standing
GaN, sapphire or silicon carbide (SiC).
The researchers note that producing longer-wavelength nitride semiconductor
LEDs is challenging due to the difficulty of producing good-quality indium
gallium nitride (InGaN) with higher indium concentration. Although growth on
silicon is well established in nitride semiconductor-based transistor
development, the researchers point out that it is only fairly recently that
similar growth methods have been applied to LED device material.
The researchers used metal-organic chemical vapor deposition (MOCVD) to grow
the initial template, grown on 2-inch silicon . The template consisted of
aluminium nitride (AlN) nucleation, 8 pairs of aluminium nitride/gallium
nitride (AlN/GaN) layers to create a superlattice (SL) as stress-balancing
interlayer, and a 2μm GaN buffer.
The researchers deposited layers of SiO2 and indium tin oxide (ITO) and
etching the ITO with hydrochloric (HCL) acid solution to form a mask, and
finally used plasma etching to form Silicon dioxide (SiO2) nanorods. The
density of nanorods was 2x109/cm2, giving a surface coverage of 35%. The
nanorods acted as a mask in GaN re-growth with reduced dislocation density and
improved crystalline quality.
Then the researchers grew the LED structure through MOCVD with re-growth of
800nm of GaN around the nanorods, an AlN/GaN SL interlayer, 2μm of n-type
GaN, a 5-period multiple quantum well (MQW), and 200nm of p-GaN. The re-grown
GaN had a dislocation density of 8x108/cm2, which was described by the
researchers as “one of the lowest values reported for GaN-on-Si
substrates, as determined by TEM”.
Materials suitable for emitting yellow (565nm) and green (505 and 530nm)
light were prepared and formed into 300μm x 300μm LED chips.
As was to be expected, the light output power (LOP) decreased as the
wavelength increased (Figure 2). At 20mA, the output at 505nm was 1.18mW. The
respective values for 530nm and 565nm were 0.30mW and 74μW, respectively.
Saturation of the light output power was achieved at 7.60mW (200mA), 2.72mW
(180mA) and 0.52mW (160mA), for the 505nm, 530nm and 565nm devices,
The researchers stated, “This is the first report of fabricated
565nm yellow InGaN/GaN MQW LEDs on a silicon substrate, and the LOP of the
505nm LEDs was much higher than that for the LEDs on Si reported in the
Apart from the improved material quality, the researchers believe that the
nanorods also provide a scattering enhancement of light extraction from the
ORNL Researchers use X-Ray Diffraction Analysis to Study Nanocrystals for LEDs
LIGHTimes News Staff
May 28, 2013...Scientists at Oak Ridge National Laboratory are reportedly using x-ray
diffraction analysis to help understand tiny crystals that could be used in
warm white LEDs. The team's most recent study is published as the inside front
cover article in the April 25 issue of Advanced
The researchers note that developing an LED that emits a broad spectrum of
warm white light on par with sunlight has proven difficult. Conventional White
LEDs produce light by passing electrons through a semiconductor material,
coupled with phosphors that glow when excited by radiation from the LED.
"It's hard to get one phosphor that makes the broad range of colors
needed to replicate the sun," commented John Budai, a scientist in ORNL's
Materials Science and Technology division. "One approach to generating
warm-white light is to hit a mixture of phosphors with ultraviolet radiation
from an LED to stimulate many colors needed for white light."
Budai is working with a team of scientists from University of Georgia and
Oak Ridge and Argonne national laboratories to understand a new group of
crystals that might produce the right blend of colors for white LEDs as well as
other uses. Zhengwei Pan's group at UGA grew the nanocrystals using europium
oxide and aluminum oxide powders as the source materials because the rare-earth
element europium is known to be a dopant, or additive, with good phosphorescent
"What's amazing about these compounds is that they glow in lots of
different colors—some are orange, purple, green or yellow," Budai
said. "The next question became: why are they different colors? It turns
out that the atomic structures are very different."
Budai and the other scientists have used x-rays from Argonne's Advanced
Photon Source to studying the atomic structure of the materials. Budai says
that two of the three types of crystal structures in the group of phosphors had
never been seen before, which can probably be attributed to the crystals' small
"Only the green ones were a known crystal structure," Budai said.
"The other two, the yellow and blue, don't grow in big crystals; they only
grow with these atomic arrangements in these tiny nanocrystals. That's why they
have different photoluminescent properties."
X-ray diffraction analysis is helping the scientists figure out the
arrangement of the atoms in each of the different crystal types. The
different-colored phosphors exhibit distinct diffraction patterns when they are
hit with x-rays, depending on the crystal structure. So the diffraction
patterns can be used to analyze the crystal structures.
"What that means in terms of how the electrons around the atoms interact
to make light is much harder," Budai said. "We haven't completely
solved that yet. That's the continuing research. We have a lot of clues, but we
don't know everything."
The atomic-scale analysis is helping the research team improve the
phosphorescent crystals. Different factors in the growth process such as
temperature, powder composition, and types of gas used can change the final
product. A fundamental understanding of all the parameters could help the team
to perfect the recipe and improve the crystals' ability to convert energy into
light. The scientists note that improving the material's luminescence
efficiency is key to making it useful for commercial LED products and other
Budai concluded, "You can keep growing the crystals and measuring them, or
you can understand why it's doing what it's doing, and figure out how to make
it better. That's what we're doing—basic research. We have to figure out
Bridgelux Closes Agreement and Expands Relationship with Toshiba to Drive GaN-on-Silicon Development
LiGHTimes News Staff
May 20, 2013...Bridgelux Inc., of Livermore California USA, a developer and manufacturer of
LED lighting technologies, has closed an agreement with Toshiba Corporation.
The agreement was originally announced on April 22, 2013 (See: Coverage),
and the companies have now completed the transfer of Bridgelux GaN-on-Silicon
technology assets to Toshiba.
The agreement includes an expanded licensing and manufacturing supply
relationship. Bridgelux says it will continue to develop and market its
GaN-on-Sapphire LED products as a fabless solid state lighting company. The
companies began their collaboration in early 2012, and later in 2012 Toshiba
became an investor in Bridgelux. As part of the previously announced agreement,
Toshiba hired Bridgelux’s GaN-on-Silicon development team. In turn,
Bridgelux reportedly retains a majority of its revenue generating operations as
a fabless LED company.
“We are thrilled to be moving into the next stage of our joint
work with Toshiba to advance GaN-on-Silicon-based solid state lighting
technologies,” said Brad Bullington, CEO of Bridgelux. “As
we outlined last month, Bridgelux will focus on commercializing, productizing
and bringing to market GaN-on-Silicon technologies alongside a proven global
scale semiconductor manufacturer. At the same time, we remain committed to our
GaN-on-Sapphire business and look forward to continuing to provide world-class
innovation and service to our customers.”
Bridgelux says it will continue developing GaN-on-Sapphire LED products which drive its operating revenue.
QD Vision Announces Achievement of 18 Percent External Quantum Efficiency
LIGHTimes News Staff
May 16, 2013...QD Vision of Lexington, Massachusetts, a developer of quantum dot based LEDs,
reports having achieved 19 cd/A efficiency and 18 percent external quantum
efficiency. QD Vision’s latest QLED performance results are currently
published in the 21
April 2013 issue of Nature Photonics. In the article, QD Vision reports
achieving 18% External Quantum Efficiency (EQE) with a color saturated red
quantum dot-based LED.
The company claims that this puts QLEDs near the fundamental efficiency
limit of the technology which the company says is 20 percent for quantum
dots.These results are two times higher efficiency than previously reported
state-of-the-art efficiency of a QLED device. QD Vision says its current and
luminous power efficiency are better than the best evaporated OLED result of
the same color coordinate, and significantly better than what
solution-processed OLEDs have thus far achieved.
In comparison, Pacific Northwest National Laboratory (PNNL) recently
reported 11 percent external quantum efficiency for a blue organic light
emitting diode (OLED) at 800 cd/m2. However Phosphor-based OLEDs are apparently
not included in the company's comparison statement.
“This paper clearly demonstrates the fundamental efficiency
advantage that QLEDs have over any other emissive display technology. Achieving
this milestone is a great breakthrough and the result of years of hard work and
dedication to achieving what others may have thought impossible,”
said QD Vision co-founder Seth Coe-Sullivan.
While at an earlier stage of development and commercialization than QD
Vision’s Color IQTM products, QD Vision says that its QLED performance is
already suitable for use in certain products that require precision color
solutions in an ultra-slim form factor, including monochrome visible and
infrared displays, and lighting devices for machine and night vision
Researchers Use Strain Engineering to Improve Green LED Light Output
LIGHTimes News Staff
May 8, 2013...Researchers from the Chinese Academy of Sciences’ Institute of
Semiconductors, Beijing, and University of Hong Kong have used strain
engineering to improve the light output of Green LEDs. The researchers improved
the light output of a 530nm green LED operating at 150 mA by 28.9 percent [Hongjian Li et al, Appl. Phys.
Express, vol6, p052102, 2013].
The researchers note that green-emitting nitride semiconductor LED
structures tend to suffer from low light output due to the difficulty in
producing the high-indium-content indium gallium nitride (InGaN) needed for
longer-wavelength light emission. In addition to the material quality
challenge, strain induced by the lattice mismatch with pure GaN leads to large
piezoelectric effects, giving electric fields that tend to pull electrons and
holes apart, reducing rates of recombination into photons (i.e. the
quantum-confined Stark effect, or QCSE), thus reducing quantum efficiency.
The Chinese team inserted a layer of lower-indium-content InGaN before the
high-In-content light-emitting layer. Simulations suggested that such a layer
could reduce the strain-dependent electric fields in the active light-emitting
multiple quantum well (MQW) structure.
MOCVD on C-plane sapphire was used to produce epitaxial material with a
low-In-content InGaN shallow quantum well (SQW) step. A 325nm helium-cadmium
laser was used to excite the photoluminescence spectra of the materials at low
temperature (85K) and room temperature (298K). One effect of the SQW was to
reduce the width of the spectral peak full-width at half maximum (FWHM) at 85K
from 16.7nm for the conventional LED material to 13.1nm for the SQW material.
The 298K measurement reduced the conventional FWHM of 20.1nm to 15.7nm. The
peak intensity was also higher with the SQW structure, therefore the SQW
material had improved crystal quality.
The peak height for the SQW material at 298K was 55.1% that at 85K. The
corresponding ratio for the conventional structure was 24.1%. The higher ratio
for the SQW material indicates a higher rate of radiative recombination and
higher internal quantum efficiency (IQE).
The electroluminescence was measured in an integrating sphere, giving light
output power–current–voltage (L–I–V) results. The
voltage performance is similar in the SQW and conventional devices. However,
the light output at 150mA is 28.9% greater in the SQW LED (49.3mW) over the
conventional device (38.4mW).
The researchers point out that improved overlap of the electron and hole
wavefunctions in the device leads to improved recombination into photons. The
external quantum efficiency (EQE) increased from 10.2–13.3% over the
conventional LED performance.
CrystAl-N Launches 2-Inch Bulk AlN
CompoundSemi News Staff
May 6, 2013...CrystAl-N, a German maker of AlN crystals is shifting its production from
1-inch to 2-inch AlN and accepting pre-orders of the new material. CrystAl-N is accepting pre-orders now. The company was founded in 2010 as a spin-off of Friedrich-Alexander-University Erlangen-Nuremberg. The company
says that its AlN substrates will boost the efficiency of deep UV LEDs, lasers
and high-power, high-frequency devices as soon as its cost-performance ratio is competitive. Furthermore CrystAl-N says that shifting production to larger
substrates will help to improve cost performance ratio.
Company CTO Boris Epelbaum commented, "Further diameter increase in our
patented tungsten based furnaces is not limited as we are using SiC as initial
Wafer polishing drastically improved as well for the AlN substrates.
"The corresponding wafers feature surface roughness of less than 0.3 nm and
are highly UV transparent," said Octavian Filip, director of wafering.
Hitachi Cable Develops Technology for Mass Production of GaN Templates
CompoundSemi News Staff
April 29, 2013...Hitachi Cable has developed a new mass-production technology for
GaN-templates. The process grows high-quality GaN single-crystal thin film on a
sapphire substrate. The company plans to start selling these templates. The
company says that using the templates as a base substrate for an epitaxial
wafer for white LEDs allows drastic improvement in productivity of white LED
epiwafers and the LED properties
MOPVE can reportedly grow a white LED epiwafer consisting of a thin active
layer and a p-type GaN layer with a total thickness of about 1μm over an
n-type GaN layer with a thickness of about 10μm, grown on a sapphire
substrate. However, it takes a long time to grow a high-quality and thick
n-type GaN layer. White LED epiwafers can be grown only about once or twice a
day at the most.
Hitachi Cable GaN-template reportedly can solve this problem because the
n-type GaN layer is already grown on the template. Hitachi Cable says that this
can reduce the time required for growth by about half compared with
conventional methods. The GaN-templates are also said to be suitable for
high-output LEDs which require large currents because they allow both low
resistance and high crystal formation,
The firm has developed single-crystal free-standing GaN substrates used for
blue-violet lasers and developed HVPE-growth technology and machines for
mass-production of GaN substrates. Template sized 2”, 4” and
6” are available with 8” templates in development.
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