Joined: 16 Mar 2004
|Posted: Fri Jan 09, 2009 3:12 pm Post subject: Nanowire LEDs Soon to Shed a New Light
|Light-emitting diodes that give a warm glow to your home or office will be available within a few years, say Swedish researchers working with nanowires.
Professor Lars Samuelson and team at Lund University are aiming to produce devices that do not cast as harsh a light as existing LEDs, and that are more efficient and longer lasting.
"We can really make the three colours - red, green and blue - with this technology and get warm LEDs," says Samuelson, who presented his research at the recent International Conference On Nanoscience and Nanotechnology in Melbourne.
Conventional LEDs are made of multiple crystalline semiconductor layers that emit light when a current passes through them, converting 30% of the electricity they receive into light.
But these LEDs are often used in small applications like torches, bicycle lights and reading lamps, rather than on a larger scale.
This is because defects in the crystal structure of the semiconductors limit their efficiency when scaled up.
"Even the commercial LEDs you buy today for your flashlight, for instance, have 10 million defects per square centimetre," says Samuelson, of the university's Nanometer Structure Consortium.
Samuelson's team have found a way to produce what they say are defect-free LEDs.
Forests of nanowires
The researchers have been making LEDs out of forests of long, thin nanowires grown from gallium arsenide and indium gallium phosphate.
Millions of these nanowires, each 2 micrometres tall and less than 200 nanometres in diameter, produce "highly perfect structures", says Samuelson.
He says they will last longer and be useful in large-scale home and office lighting, with an efficiency of around 50%, more efficient than existing incandescent or fluorescent lighting.
By comparison, an incandescent light bulb is only 4% efficient, a compact fluorescent 25%.
The nanowire LEDs are brighter than existing LEDs and can emit light more easily to their surrounds, Samuelson says.
They can be tuned to give warm colours, by adjusting the concentration of different elements in the crystalline structure.
New crop of LEDs
Samuelson says the research has been funded by Swedish and European research programs and he is involved in a start-up company to commercialise large-scale LED lighting within the next three years.
Other researchers are working towards warmer LEDs for use in home lighting using methods other than nanowires.
But nanowire LEDs are expected to be the most efficient, says Australian nano-engineering expert Professor Chennupati Jagadish of the Australian National University's Research School of Physical Sciences and Engineering.