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Nanowires afford LEDs better light, energy-savings

Posted: 26 Jun 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Niels Bohr Institute? LED? nanowire? X-ray microscopy?

A team of researchers from Denmark's Niels Bohr Institute has demonstrated that LEDs made from nanowires will use less energy and provide better light. They studied nanowires using X-ray microscopy and with this method the researchers were able to pinpoint exactly how the nanowire should be designed to give the best properties.

Nanowires are small about 2?m high and 10nm to 500nm in diameter. Nanowires for LEDs are made up of an inner core of gallium nitride (GaN) and a layer of indium-gallium-nitride (InGaN) on the outside, both of which are semiconducting materials.

The light in such a diode is dependent on the mechanical strain that exists between the two materials and the strain is very dependent on how the two layers are in contact with each other. We have examined a number of nanowires using X-ray microscopy and even though the nanowires should in principle be identical, we can see that they are different and have very different structure, explained Robert Feidenhansl, professor and head of the Niels Bohr Institute at the University of Copenhagen.

The studies were performed using nanoscale X-ray microscopy in the electron synchrotron at DESY in Hamburg, Germany. The method is time consuming and the results are often limited to very few or even a single study subject. But the researchers have managed to measure a series of upright nanowires all at once using a special design of a nanofocused X-ray without destroying the nanowires in the process.

X-ray images of nanowire

The X-ray images of each nanowire show the distribution of the scattering intensity and the mechanical strain in the core of gallium-nitride and the shell of indium-gallium-nitride. The strain shows that the shell fits perfectly with the core.

We measured 20 nanowires and when we saw the images, we were very surprised because you could clearly see the details of each nanowire. You can see the structure of both the inner core and the outer layer. If there are defects in the structure or if they are slightly bent, they do not function as well. So we can identify exactly which nanowires are the best and have the most efficient core/shell structure, stated Tomas Stankevic, a PhD student in the research group neutron and X-ray scattering at the Niels Bohr Institute at the University of Copenhagen.

Feidenhansl said nanowires will provide a more natural light in LEDs and they will use much less power. In addition, they could be used in smartphones, TVs and many forms of lighting.

The researchers expect that the nanowires may be in use within five years.

- Paul Buckley
??EE Times Europe

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