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Nanowires could provide the LEDs of the future

24 June 2015

The latest research from the Niels Bohr Institute in Denmark shows that LEDs made from nanowires would use less energy and provide a better light.

A series of nanowires were scanned in the nanofocused X-ray, while the reflections from the different crystal planes of the nanowires were measured (image: Tomas Stankevic/Niels Bohr Institute/University of Copenhagen)

The researchers studied nanowires using X-ray microscopy and with this method they are able to determine exactly how the nanowire should be designed in order for it to provide the desirable properties. An article describing this work is published in the journal, ACS Nano.

The nanowires in question measure about 2 micrometres long by 10-500 nanometres in diameter. For LEDs these 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," says Professor Robert Feidenhans'l, who heads up the Niels Bohr Institute at the University of Copenhagen.

"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."

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 (image: Tomas Stankevic/Niels Bohr Institute/University of Copenhagen

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

"We measured 20 nanowires and when we saw the images, we were very surprised because you could clearly see the details of each nanowire," says Tomas Stankevic, a PhD student in Feidenhans'l's research group. "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."

The nanowires are produced by a company in Sweden and this new information can be used to tweak the layer structure in the nanowires. Professor Feidenhans'l believes there is great potential in such nanowires, as they could provide a more natural light in LEDs and use much less power. His team thinks nanowire based LEDs could be in use within five years.

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