“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.”
Lead researcher on the project, Dr Slava Kachkanov
Figure 1. (a) and (b) show projections of the RLP onto the Qy-Qz plane for sample A and sample B measured for ω=19.424° and ω=19.357° respectively, (c) and (d) are projections of the RLP on the Qx-Qz plane for the same samples. The inclined and vertical red lines in (a) and (b) indicate lattice constants for relaxed InGaN alloys and a lattice contstant (3.189 Å) for unstrained GaN. The “tails” of RLPs correspond to the “seed” InGaN.
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.
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.
Figure 2. The X-ray diffraction intensity speckle pattern for sample A observed during spatial scan. Note that the image is not transformed to reciprocal space.
‘InGaN epilayer characterization by microfocused x-ray reciprocal space mapping’
V. Kachkanov, I. P. Dolbnya, K. P. O’Donnell, R. W. Martin, P. R. Edwards, and S. Pereira
Appl. Phys. Lett. 99, 181909 (2011)
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