We all know LED as being the flagship of green lighting, but what if those so-called “efficient” LEDs turned out to be even more energy-effective under certain conditions? The Kyoto University, in collaboration with Stanley Electric Co Ltd found a way to increase the emission intensity of silicon-based thin films by several times.
“We developed a technology to increase the emission intensity of, for example, white LEDs,” a Stanley Electric representative said at the 71th Autumn Meeting 2010 of the Japan Society of Applied Physics.
Researchers from the two institutions created a porous thin film of silicon nanocrystals and deposited it on a silicon substrate. On top of that they deposited gold, after roughening the previously deposited surface, thus creating a film 30 micrometers thick.
To test their achievement, the researchers then irradiated the film with a 405 nm laser, and found out the film emitted light with an intensity several times stronger than it had emitted without the gold deposition. Also known as “light emitting silicon”, the gold-covered silicon nanocrystals have an external quantum efficiency of 19.8%.
However, when they did the same test on a fine, not roughened Si thin film, but on which they still deposited the gold, the yielded results were several percents lower, just like they hadn’t treated the surface with gold.
“We consider that exciton hopping and surface plasmon resonance are occurring at the same time,” says the Stanley representative, explaining the reason why roughened surfaces yielded better results than the fine ones.