SYNTHESIS OF THICK GALLIUM NITRIDE LAYERS BY METHOD OF MULTI-STAGE GROWTH ON SUBSTRATES WITH COLUMN STRUCTURE
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For citation: Mynbaeva M.G., Kirilenko D.A., Sitnikova A.A., Kremleva A.V., Nikolaev V.I., Mynbaev K.D., Odnoblyudov M.A., Lipsanen H., Bougrov V.E., Romanov A.E. Synthesis of thick gallium nitride layers by method of multi-stage growth on substrates with column structure. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2016, vol. 16, no. 6, pp. 1048–1055. doi: 10.17586/2226-1494-2016-16-6-1048-1055
Subject of Research.The paper deals with processes of formation and transformation of defects during multi-stage growth of thick gallium nitride layers with hydride vapor phase epitaxy on GaN/Al2O3 substrates with buried column pattern formed with the use of metal-organic vapor phase epitaxy. Methods. The growth of initial GaN layers was performed with the use of metal-organic vapor phase epitaxy. On the surface of the initial layers columns with the height of 800 nm were generated by means of ion etching. These columns were overgrown with 3-4 µm-thick GaN layers. On thus formed substrate multi-stage growth of GaN layers was performed with the use of hydride vapor-phase epitaxy. The total thickness of GaN layers was 100-1500 µm. The grown layers were studied by optical and electron microscopy and Raman spectroscopy. Main Results. Density of threading dislocations in the layers grown by hydride vapor-phase epitaxy was (3-6)·107 cm-2, that was one order of magnitude lower than in the used substrate, and two to three orders lower than dislocation density in typical GaN layers grown on commercial sapphire substrates. Raman spectroscopy data were indicative of low level of mechanical stress in the layers and their high structural uniformity. It was established that under multi-stage growth conditions, non-catastrophic cracks (those that do not cause sample destruction) are able to transform into macropores and appear to be an important st ructural element, serving to stress relaxation in the bulk of thick gallium nitride layers grown on foreign substrates. Practical Relevance. The results of the study can be used in the development of III-nitride heterostructures for optoelectronics and high-power and high-frequency microelectronics.
Acknowledgements. This work was supported by the Russian Science Foundation (RSF Grant No.14-29-00086)
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Fig. 1. Scanning electron microscopy image of the surface and cross-section of GaN/ Al2O3 plate with the generated column structure
a) b) c)
Fig. 3. Process dynamics Illustration (a-c) of reducing the number of cracks in multistage process of the chloride-hydride epitaxy. The arrow denotes one of the cracks that is evolutionary up to complete refilling in the last epitaxial cycle
Fig. 4. The image by transmission electron microscopy of the GaN layer cross section, showing macropore and threading dislocation that has changed the direction of propagation near the wall of the macropore
Fig. 5. Photos of the structures with GaN layers with a thickness of 100 µm (a) and 1000 µm (b) grown by chloride-hydride epitaxy method. The diameter of the plates is equal to 5.08 cm
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