New way to extract light from semiconductors could lead to ultra-high efficiency LEDs

May 14, 2010 by Lisa Zyga report
The illustration in (a) shows evanescent waves coupling at two interfaces on the flat planes of a ridge. Figure (b) shows the simulated electromagnetic field intensity of the structure. Image credit: AIST.

(PhysOrg.com) -- By fabricating ridges coated with silicon dioxide (SiO2) on the surface of a semiconductor, scientists from the National Institute of Advanced Industrial Science and Technology (AIST) in Japan have shown how to extract light from a semiconductor with an extremely high efficiency. The new technique could lead to the development of low-cost, ultra-high efficiency LEDs for lighting and display applications. With the widespread use of LEDs, researchers estimate that global electricity consumption could be reduced by 10% or more, which could save about $120 billion over the next 20 years.

As the researchers explain, the key to improving an LED’s lies in extracting the light generated in the semiconductor with the highest efficiency possible. However, the strong internal reflection in the semiconductor makes efficient light extraction very difficult, since light tends to remain inside the semiconductor. Most techniques to improve the light extraction efficiency have high production costs, but finding a highly efficient, low-cost light extraction technique is essential for popularizing LED lighting.

The AIST researchers, XueLun Wang and Mutsuo Ogura, were able to design a semiconductor to take advantage of the effects of evanescent waves for improving light extraction efficiency. As the scientists explain, evanescent waves are a special kind of light existing only near a reflection interface. When two evanescent waves meet, they are efficiently transformed into light.

In their experiments, the researchers fabricated a GaAs/AlGaAs nanostructure with V-shaped grooves and even smaller ridges between the grooves. They then deposited a 150-nm-thick layer of SiO2 onto the nanostructure. This design enabled evanescent waves to form and couple at the semiconductor-SiO2 and SiO2-air interfaces on flat planes at the tops of the ridges, resulting in an increase of the amount of light that could be extracted.

studies revealed that the SiO2-coated semiconductor’s light-emitting layer at the ridges was enhanced by a factor of 1.7. According to a press release, the light-extraction efficiency builds upon and exceeds the 50% efficiency of a similar technique, although the exact efficiency of the current design is not mentioned. In contrast, uncoated light-emitting semiconductor materials deposited on flat substrates only enable a few percent of the light generated in the semiconductor to be extracted; for example, GaAs has only a 2% efficiency.

One advantage of the new design is that it doesn’t require any significant changes to the conventional LED fabrication process, which should keep fabrication costs low. The method could also be used with other materials, such as indium tin oxide or zinc oxide as the coating, and AlGaInP-based and GaN-based materials, which can be used to develop visible LEDs with ultra-high light extraction efficiency.

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Alizee
May 14, 2010
This comment has been removed by a moderator.
kaasinees
1.5 / 5 (2) May 14, 2010
Old-shaped ineffective LED should be banned in European Union soon..

I totally agree with this notion. Any improved technology of this magnitude should be applied immediately, it might cost a bit but will repay itself in the end.
frajo
3 / 5 (2) May 14, 2010
Old-shaped ineffective LED should be banned in European Union soon..
Why?
jamey
5 / 5 (2) May 14, 2010
Old-shaped ineffective LED should be banned in European Union soon..

I totally agree with this notion. Any improved technology of this magnitude should be applied immediately, it might cost a bit but will repay itself in the end.


Not necessarily. What if, before it has a chance to pay itself off, something even cheaper comes along, and gets mandated.
Daein
5 / 5 (1) May 14, 2010
Just let the free market take it's course. If it's cheaper and better it will rapidly replace its predecessors.
kaasinees
1 / 5 (1) May 15, 2010
Old-shaped ineffective LED should be banned in European Union soon..

I totally agree with this notion. Any improved technology of this magnitude should be applied immediately, it might cost a bit but will repay itself in the end.


Not necessarily. What if, before it has a chance to pay itself off, something even cheaper comes along, and gets mandated.


Led's have been around forever. It is only recently they have been developed enough to make screens with it. Even if it is only 5 years before they make them better 30billion is saved on electricity also billions of medical bills because of pollution. Also quite obvious led will becheap in such magnitude that competitive products will become obsolete. This all means a one time investment pays offvery well in maybe even 2 years. Even for the government it would be the best investment they could ever make to save money.

Let the free market take its course? Sure just wait 5 years till they really use this.
MNIce
5 / 5 (1) May 16, 2010
There's no need for a government mandate if AIST advertises reasonable license fees for the technology. LED manufacturers will race to get this into production if it is this good. The demand for cheaper, brighter, more efficient LEDs is already strong.
Anynomouse
1 / 5 (1) May 16, 2010
How about instead of adding new subsidies for efficient technology, we remove old subsidies that promote waste?

i.e. - I pay hundreds in property taxes for roads and bridges, but I ride a bicycle to work. How much of the 600B US defense budget is wrapped up one way or other in oil? How much do oil users pay for this? Zero.

Give me a thousand a year back in income and property taxes and raise gas taxes 1.50$ per US Gallon. That's still way lower than Europe.