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Seeking the light fantastic

02 April 2012

Facilities at the Diamond Light Source are helping researchers to develop the products of tomorrow - in this case bright white light LEDs that one day will replace incandescent and fluorescent domestic light bulbs.

With the phase-out of incandescent light bulbs becoming more common around the world, there is a need to investigate more efficient and robust alternatives. Thanks to their low energy consumption, prolonged life, small size and reliability, LEDs are seen as an attractive option. But they are not quite ready to take over from the light bulb yet. A bright white LED powerful enough to light up a room is currently very expensive. New research, which takes advantage of facilities available at the Diamond Light Source, is a step towards making white LEDs a viable general lighting option.

At Diamond Light Source, a team of researchers has used the Diamond synchrotron's intense X-rays to probe the structure of the light-emitting material used in blue and green light-emitting diodes (LEDs), indium gallium nitride (InGaN). Their research (published in the journal Applied Physics Letters) revealed the growth pattern of the green-light-emitting form of the material - information that will help optimise this technology. Lead researcher, Dr Slava Kachkanov takes up the story:

"The structural information we collected during our measurements using the B16 Test beamline at Diamond showed us that as the thin-films of InGaN grow, the atoms form distinctive nanosized islands. This told us that the material follows something called the Volmer-Weber growth pattern. This was not clear before, so we can now apply this knowledge to improve the techniques used to grow this material to ensure optimal results.

"InGaN produces blue light - no problem. Now that we have a better understanding of the InGaN growth process, we can work on improving the quality of green and red light emission. The combination of red, green and blue would create a white light without the need for low efficiency phosphors, which are currently used in white LEDs."

Gaining a better understanding of InGaN and its structure could have an impact on a number of other industries where gallium nitride (GaN) plays an important role. For instance GaN holds great potential for use in high-power microwave generators and amplifiers which can be used in microwave ovens, radar systems and even on synchrotrons.

Dr Slava and his team used a technique called microfocus X-ray diffraction to study the thin-films of InGaN. Beamline B16 was well-suited to the job due to its high-performing compound refractive X-ray optics (CRLs), equipment capable of focusing X-rays down to a few micrometers in size, which is essential to probe selected volumes of thin InGaN layers. The finely tuned X-rays were focused onto the material and deflected by the atoms within it. The resulting diffraction pattern informed the group of the crystal structure of their material. 

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