July 20th, 2008
Posted by Roland Piquepaille @ 9:42 am
You
all know that incandescent bulbs are pretty inefficient, converting
only 10% of electricity into light — and 90% into heat. Light-emitting
diodes, or LEDs, could soon replace incandescent and compact
fluorescent bulbs in our homes. They are more efficient and
environmentally friendly. But LED lights are currently too expensive
because they are using a sapphire-based technology. Now, Purdue
University researchers have found a way to build low-cost and bright LEDs for home lighting.
According to the researchers, the LED lights now on the market cost
about $100 while LED lights based on their new technology could be
commercially available within a couple of years for a cost of about $5.
It would also help to cut our electricity bill by about 10%, but read
more…
You can see above how “Timothy Sands, at left, director of Purdue’s
Birck Nanotechnology Center in Discovery Park, and graduate student
Mark Oliver, operate a ‘reactor’ in work aimed at perfecting
solid-state lighting, a technology that could cut electricity
consumption by 10 percent if widely adopted.” (Credit: Purdue News
Service; photo by David Umberger) Here is a link to a larger version of this photo.
This research work has been led by Timothy Sands, Professor of Materials Engineering at Purdue University. Sands is also the Director of the Birck Nanotechnology Center at Discovery Park and manages the Heterogeneous Materials Integration Research Group. Several members of this group participated to this project, including Mark Oliver, Graduate Research Assistant.
The research team is not using expensive sapphire-based technology, but cheaper silicon-based one.
“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. 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.”
And here are additional details provided by Emil Venere from Purdue
University. “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.”
For more information, this research work has been published in Applied Physics Letters
under the title “Organometallic vapor phase epitaxial growth of GaN on
ZrN/AlN/Si substrates” (Volume 93, Issue 2, Article 023109, July 14,
2008).
And for your ‘reading’ pleasure, here is the abstract.
“An intermediate ZrN/AlN layer stack that enables the epitaxial growth
of GaN on (111) silicon substrates using conventional organometallic
vapor phase epitaxy at substrate temperatures of ~1000 °C is reported.
The epitaxial (111) ZrN layer provides an integral back reflector and
Ohmic contact to n-type GaN, whereas the (0001) AlN layer serves as a
reaction barrier, as a thermally conductive interface layer, and as an
electrical isolation layer. Smooth (0001) GaN films less than 1 μm
thick grown on ZrN/AlN/Si yield 0002 x-ray rocking curve full width at
half maximum values as low as 1230 arc sec.”
If I had only read this paragraph, I doubt I would have published this post…
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