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LED breakthrough may revolutionize lighting

R

rpautrey2

Jan 1, 1970
0
LED breakthrough may revolutionize lighting
http://eartheasy.com/article_led_breakthrough.html


Purdue researchers achieve LED production breakthrough which clears
the way for low-cost, high-efficiency lighting.

LED light bulbs are about four times more efficient than conventional
incandescent lights and, because they contain no mercury, more
environmentally friendly than compact fluorescent bulbs. LEDs are also
longer lasting than conventional lighting, lasting perhaps as long as
15 years before burning out.

"LED technology has the potential of replacing all incandescent and
compact fluorescent bulbs, which would have dramatic energy and
environmental ramifications," said Timothy D. Sands, the Basil S.
Turner Professor of Materials Engineering and Electrical and Computer
Engineering at Purdue University.

But LED lights now on the market are prohibitively expensive, in part
because they are created on a substrate, or first layer, of sapphire.
The Purdue researchers have solved this problem by developing a
technique to create LEDs on low-cost, metal-coated silicon wafers,
said Mark H. Oliver, a graduate student in materials engineering who
is working with Sands.

LEDs designed to emit white light are central to solid-state lighting,
semiconducting devices made of layers of materials that emit light
when electricity is applied. Conventional lighting generates light
with hot metal filaments or glowing gasses inside glass tubes.

The LEDs have historically been limited primarily to applications such
as indicator lamps in electronics and toys, but recent advances have
made them as bright as incandescent bulbs.

The light-emitting ingredient in LEDs is a material called gallium
nitride, which is used in the sapphire-based blue and green LEDs,
including those in traffic signals. The material also is used in
lasers in high-definition DVD players. The sapphire-based technology,
however, is currently too expensive for widespread domestic-lighting
use, costing at least 20 times more than conventional incandescent and
compact fluorescent light bulbs.

One reason for the high cost is that the sapphire-based LEDs require a
separate mirrorlike collector to reflect light that ordinarily would
be lost. In the new silicon-based LED research, the Purdue engineers
"metallized" the silicon substrate with a built-in reflective layer of
zirconium nitride.

"When the LED emits light, some of it goes down and some goes up, and
we want the light that goes down to bounce back up so we don't lose
it," said Sands, the Mary Jo and Robert L. Kirk Director of the Birck
Nanotechnology Center in Purdue's Discovery Park.

Ordinarily, zirconium nitride is unstable in the presence of silicon,
meaning it undergoes a chemical reaction that changes its properties.

The Purdue researchers solved this problem by placing an insulating
layer of aluminum nitride between the silicon substrate and the
zirconium nitride.

"One of the main achievements in this work was placing a barrier on
the silicon substrate to keep the zirconium nitride from reacting,"
Sands said.

Until the advance, engineers had been unable to produce an efficient
LED created directly on a silicon substrate with a metallic reflective
layer.
Until the advance, engineers had been unable to produce an efficient
LED created directly on a silicon substrate with a metallic reflective
layer.

The Purdue team used a technique common in the electronics industry
called reactive sputter deposition. Using the method, the researchers
bombarded the metals zirconium and aluminum with positively charged
ions of argon gas in a vacuum chamber. The argon ions caused metal
atoms to be ejected, and a reaction with nitrogen in the chamber
resulted in the deposition of aluminum nitride and zirconium nitride
onto the silicon surface. The gallium nitride was then deposited by
another common technique known as organometallic vapor phase epitaxy,
performed in a chamber, called a reactor, at temperatures of about
1,000 degrees Celsius, or 1,800 degrees Fahrenheit.

As the zirconium nitride, aluminum nitride and gallium nitride are
deposited on the silicon, they arrange themselves in a crystalline
structure matching that of silicon.

"We call this epitaxial growth, or the ordered arrangement of atoms on
top of the substrate," Sands said. "The atoms travel to the substrate,
and they move around on the silicon until they find the right spot."

This crystalline formation is critical to enabling the LEDs to perform
properly.

"It all starts with silicon, which is a single crystal, and you end up
with gallium nitride that's oriented with respect to the silicon
through these intermediate layers of zirconium nitride and aluminum
nitride," Sands said. "If you just deposited gallium nitride on a
glass slide, for example, you wouldn't get the ordered crystalline
structure and the LED would not operate efficiently."

Using silicon will enable industry to "scale up" the process, or
manufacture many devices on large wafers of silicon, which is not
possible using sapphire. Producing many devices on a single wafer
reduces the cost, Sands said.

Another advantage of silicon is that it dissipates heat better than
sapphire, reducing damage caused by heating, which is likely to
improve reliability and increase the lifetime of LED lighting, Oliver
said.

The widespread adoption of solid-state lighting could have a dramatic
impact on energy consumption and carbon emissions associated with
electricity generation since about one-third of all electrical power
consumed in the United States is from lighting.

The widespread adoption of solid-state lighting could have a dramatic
impact on energy consumption and carbon emissions associated with
electricity generation since about one-third of all electrical power
consumed in the United States is from lighting.

"If you replaced existing lighting with solid-state lighting,
following some reasonable estimates for the penetration of that
technology based on economics and other factors, it could reduce the
amount of energy we consume for lighting by about one-third," Sands
said. "That represents a 10 percent reduction of electricity
consumption and a comparable reduction of related carbon emissions."

Incandescent bulbs are about 10 percent efficient, meaning they
convert 10 percent of electricity into light and 90 percent into
heat.

"Its actually a better heater than a light emitter," Sands said.

By comparison, efficiencies ranging from 47 percent to 64 percent have
been seen in some white LEDs, but the LED lights now on the market
cost about $100.

"When the cost of a white LED lamp comes down to about $5, LEDs will
be in widespread use for general illumination," Sands said. "LEDs are
still improving in efficiency, so they will surpass fluorescents.
Everything looks favorable for LEDs, except for that initial cost, a
problem that is likely to be solved soon."

He expects affordable LED lights to be on the market within two years.

Two remaining hurdles are to learn how to reduce defects in the
devices and prevent the gallium nitride layer from cracking as the
silicon wafer cools down after manufacturing.

"The silicon wafer expands and contracts less than the gallium
nitride," Sands said. "When you cool it down, the silicon does not
contract as fast as the gallium nitride, and the gallium nitride tends
to crack."

Sands said he expects both challenges to be met by industry.

"These are engineering issues, not major show stoppers," he said. "The
major obstacle was coming up with a substrate based on silicon that
also has a reflective surface underneath the epitaxial gallium nitride
layer, and we have now solved this problem."

The research, based at the Birck Nanotechnology Center and funded by
the U.S. Department of Energy through its solid-state lighting
program, is part of a larger project at Purdue aimed at perfecting
white LEDs for lighting.


References:
Science Daily
Adapted from materials provided by Purdue University.
Purdue University (2008, July 21). Advance Brings Low-cost, Bright LED
Lighting Closer To Reality. ScienceDaily.



http://eartheasy.com/article_led_breakthrough.html
 
D

Don Klipstein

Jan 1, 1970
0
LED breakthrough may revolutionize lighting
http://eartheasy.com/article_led_breakthrough.html

Purdue researchers achieve LED production breakthrough which clears
the way for low-cost, high-efficiency lighting.

LED light bulbs are about four times more efficient than conventional
incandescent lights

Same as CFLs - and that is for better than is achieved by most LED
lighting products.
and, because they contain no mercury, more
environmentally friendly than compact fluorescent bulbs.

Although this is true when you have LED outperforming CFL (which is not
common in lighting), keep in mind that CFL is better for the environment
than incandescent - and close to a draw if even considering only mercury!
Coal combustion is a huge source of mercury pollution, and CFLs achieving
6,000 hour life when replacing incandescents as low as 60 watts will
actually not increase mercury pollution even if their recycling rate is
zero!
And to improve upon that - www.lamprecycle.org! Also, Home Depot takes
worn-out CFLs for proper disposal!
LEDs are also longer lasting than conventional lighting, lasting perhaps
as long as 15 years before burning out.

"Perhaps as long as"?

What about the widely-touted 100,000 hours?

What about better major brand white ones achieving 50,000 hours before
fading by at least 30% "with good treatent" including heatsinking to
extent of achieving temperature significantly cooler than "dataseet
temperature limit"?

Also, rated efficiency tends to be achieved when either "heatsinkable
surface" or the hottest internal point of the chip(s) of the LED is cooled
to 25 degrees C!
"LED technology has the potential of replacing all incandescent and
compact fluorescent bulbs, which would have dramatic energy and
environmental ramifications," said Timothy D. Sands, the Basil S.
Turner Professor of Materials Engineering and Electrical and Computer
Engineering at Purdue University.

But LED lights now on the market are prohibitively expensive, in part
because they are created on a substrate, or first layer, of sapphire.
The Purdue researchers have solved this problem by developing a
technique to create LEDs on low-cost, metal-coated silicon wafers,
said Mark H. Oliver, a graduate student in materials engineering who
is working with Sands.

It has been brought to my attention a few times already over the past
many years how there were supposed to be in-the-works good-high-efficiency
LED chips with silicon substrate!
LEDs designed to emit white light are central to solid-state lighting,
semiconducting devices made of layers of materials that emit light
when electricity is applied. Conventional lighting generates light
with hot metal filaments or glowing gasses inside glass tubes.

The LEDs have historically been limited primarily to applications such
as indicator lamps in electronics and toys, but recent advances have
made them as bright as incandescent bulbs.

The light-emitting ingredient in LEDs is a material called gallium
nitride, which is used in the sapphire-based blue and green LEDs,
including those in traffic signals. The material also is used in
lasers in high-definition DVD players. The sapphire-based technology,
however, is currently too expensive for widespread domestic-lighting
use, costing at least 20 times more than conventional incandescent and
compact fluorescent light bulbs.

One reason for the high cost is that the sapphire-based LEDs require a
separate mirrorlike collector to reflect light that ordinarily would
be lost.

Cree Inc. has been for a goodly few years already been achieving such
LEDs with silicon carbide substrate - and even appears to me to have
achieved transparent silicon carbide!

A mirror under the chip is dirt-cheap!

Incandescent bulbs are about 10 percent efficient, meaning they
convert 10 percent of electricity into light and 90 percent into
heat.

That good? I have yet to find a 120V 100W A19 incandescent even rated
1750 lumens of 7-+ efficiency at converting input to electromagnetic
radiation of wavelengtths 400-700 nm!
"Its actually a better heater than a light emitter," Sands said.

By comparison, efficiencies ranging from 47 percent to 64 percent have
been seen in some white LEDs, but the LED lights now on the market
cost about $100.

Please tell me mfr, part number and supplier for any white LED that I
can buy that achieves 47-64% efficiency, along with conditions for
achieving such efficiency. That sounds to me like about 140-190
lumens/watt.
"When the cost of a white LED lamp comes down to about $5, LEDs will
be in widespread use for general illumination," Sands said. "LEDs are
still improving in efficiency, so they will surpass fluorescents.

So surpassing of fluorescents has yet to be achieved? I thought that
has been recently achieved already by small margin with lower wattages
with great upfront-cost-per-whatever.
Everything looks favorable for LEDs, except for that initial cost, a
problem that is likely to be solved soon."

He expects affordable LED lights to be on the market within two years.

Two remaining hurdles are to learn how to reduce defects in the
devices and prevent the gallium nitride layer from cracking as the
silicon wafer cools down after manufacturing.

"The silicon wafer expands and contracts less than the gallium
nitride," Sands said. "When you cool it down, the silicon does not
contract as fast as the gallium nitride, and the gallium nitride tends
to crack."

Sands said he expects both challenges to be met by industry.

"These are engineering issues, not major show stoppers," he said.

Read the posting that I quoted from if you need to see everything that I
snipped. And buyer beware!

- Don Klipstein ([email protected])
 
E

Eeyore

Jan 1, 1970
0
rpautrey2 said:
LED breakthrough may revolutionize lighting
http://eartheasy.com/article_led_breakthrough.html

Don't take press releases from such sites without a pinch of salt.

It'll be years before they become mainstream and many false claims have
already been made along the route.

Incidentally, the mercury claim is essentially bogus and purely there to
appeal to those who succumb to the 'fear factor'. Making semiconductors is
pretty nasty too.

Graham
 
D

Don Klipstein

Jan 1, 1970
0
Don't take press releases from such sites without a pinch of salt.

It'll be years before they become mainstream and many false claims have
already been made along the route.

Incidentally, the mercury claim is essentially bogus and purely there to
appeal to those who succumb to the 'fear factor'. Making semiconductors is
pretty nasty too.

I would like to know where that one gets 47-64% efficiency for "some
white LEDs".

I have one piece of hard data for number of lumens in 1 watt of "white
LED light": 331. This figure will vary with spectral characteristics.

http://ledsmagazine.com/articles/news/3/11/22/1

That LED achieved 138 lumens/watt while achieving 41.7% conversion
efficiency. (The LED makers like to call that "wallplug efficiency",
even though that is milliwatts of light out per 100 milliwatts delivered
to the LED, not per 100 milliwatts from the power supply.)

It appears to me that the 150 lumen/watt laboratory prototype developed
afterwards achieves conversion efficiency somewhere around 45%.

That article on the 41.7% efficient white LED does mention 63.3% quantum
efficiency for a blue LED chip. That means 633 photons emitted per 1,000
electrons pushed through. However, each photon has less energy than was
expended to push each electron through - in the ballpark of 2.7 eV vs. 3.2
eV.
Meanwhile, the phosphor that is added to make a blue LED into a white
one has both quantum loss and Stokes loss. Because of the Stokes loss,
the average energy per photon from a usual white LED is more like 2.3-2.35
eV.

And the Osram laboratory prototype that I mentioned in a different
thread achieved 170 lumens/watt when very greatly underpowered. Also,
that one's light is more yellowish/greenish than that of most other white
LEDs, so its light probably has more than 331 lumens per radiated watt.
So that looks to me like about 50% conversion efficiency at the fairly
severe degree of underpowering that results in maximum efficiency.

Yes, I see a fair amount of hype in press releases, and also by LED
lighting product manufacturers and sellers.

- Don Klipstein ([email protected])
 
R

rpautrey2

Jan 1, 1970
0
Don,
I've been using CFL's and other flourescent
lighting for many years. My experience with
the CFL's is some don't come on instantly
and their reliability isn't what it's claimed to be.
I'm looking forward to LED lighing. I'm pleased with
the light and reliability of my LED flashlights and lanterns.

Paul
 

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