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Honeycomb defects in GaN crystals visualised at the ESRF


Researchers from Fraunhofer Institute for Applied Solid State Physics used X-ray Bragg diffraction imaging techniques to characterise unusual honeycomb defects in gallium nitride crystals.

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GaN, Gallium nitride is a semiconductor material used in LEDs and lasers, and with promise for use as transistors in telecommunications networks under extreme conditions. It is an extremely hard material, and its crystals are challenging to make, they are brittle, and they often contain a high level of defects. A breakthrough was achieved with GaN crystals grown ammonothermally, that is crystallisation from supercritical ammonia, as the crystals produced exhibit a dramatically reduced density of defects. The characterisation of defects is very important because they can be detrimental to the use of crystals in applications. Characterisation of defects requires high spatial and angular resolution techniques such as the Bragg diffraction imaging techniques developed at the ESRF. These techniques were able to show that aligned bundles of dislocations are associated with faintly misoriented (seconds of arc) regions, and revealed defect clusters with hexagonal shapes that had never been observed before.

Researchers from the Fraunhofer Institute for Applied Solid State Physics have presented the results of their work at ESRF beamline BM05 in a publication. They used X-ray Bragg diffraction imaging techniques along with etching of the crystal surface to reveal the structure of these honeycomb like defect clusters, which vary in size from 0.05 mm to 2 mm and contain a large concentration of edge type threading dislocations forming bundles located at the corners of the hexagons. The size of the honeycomb defect clusters correlates with the number of dislocations in the bundles.


Lang X-ray topography (L-XRT) topograph of a semi-insulating GaN substrate with honeycomb disslocations (HCDs) marked by red hexagons with an enlargement on the right of the one marked HCD-A.


Kirste, L.; Tran Thi Caliste, T.N.; Weyher, J.L.; Smalc-Koziorowska, J.; Zajac, M.A.; Kucharski, R.; Sochacki, T.; Grabianska, K.; Iwinska, M.; Detlefs, C.; Danilewsky, A.N.; Bockowski, M.; Baruchel, J. Large-Scale Defect Clusters with Hexagonal Honeycomb-like Arrangement in Ammonothermal GaN Crystals. Materials 15, 6996 (2022); doi: 10.3390/ma15196996