doi: 10.17586/2226-1494-2016-16-6-1038-1047


DISTRIBUTION OF DISLOCATIONS IN AlN CRYSTALS GROWN ON EVAPORATING SiC SUBSTRATES

T. S. Argunova, M. Y. Gutkin, K. D. Shcherbachev, O. P. Kazarova, E. N. Mokhov, J. Je


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For citation: Argunova T.S., Gutkin M.Yu., Shcherbachev K.D., Kazarova O.P., Mokhov E.N., Jung Ho Je. Distribution of dislocations in AlN crystals grown on evaporating SiC substrates. Scientific and Technical Journal of Information Technologies, Mechanics and Optics, 2016, vol. 16, no. 6, pp. 1038–1047. doi: 10.17586/2226-1494-2016-16-6-1038-1047

Abstract

By the use of high-resolution X-ray diffractometry and synchrotron radiation topography, the distribution of dislocations in AlN crystals grown on evaporating SiC substrates is studied. The growth of AlN layer in one process with the evaporation of SiC substrate gave the possibility to prevent the relaxation of thermal stresses through cracking of AlN during cooling the structure. The continuous 0.2-1.5 mm thick plates were used as the model objects for the study of dislocation structure near the AlN/SiC interface. Analysis of the broadening of the Bragg reflection peaks, the shape of scattering maps in reciprocal space and topographs showed that dislocations formed the mosaic structure, different from the distribution of threading dislocations in GaN epilayers. A theoretical model for misfit strain relaxation in the growing AlN layer is suggested. The results enable to clarify the dislocation processes during sublimation growth of industrial quality AlN crystals.  


Keywords: dislocations, aluminum nitride, silicon carbide, crystals, X-ray diffractometry, X-ray topography, synchrotron radiation, epitaxial films, evaporation of substrates, thermal stresses, misfit stresses, stress relaxation, mosaic structure

Acknowledgements. M. Yu. Gutkin acknowledges the Russian Science Foundation (grant RSF No. 14-29-00086) for support in the development of a theoretical model of misfit stress relaxation in AlN crystals, and E. N. Mokhov acknowledges the Russian Science Foundation (grant RSF No. 16–42–01098) for support in carrying out experimental research.

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PICTURES

 Fig.1  X-ray topograms obtained in the synchrotron radiation from AlN crystal with evaporated SiC substrate. Polychromatic radiation. Laue geometry. Kodak M100 film. Images of borders seem double, because the emulsion layer has been coated on both sides of the film (a). Monochromatic radiation with energy E = 20 keV. Bragg geometry.  CCD detector with pixel size equal to 16 µm (b, c)

 

 Fig.2. Triple-crystal intensity distribution curves depending on wangle measured by w- and 2q–w-scanning in 0004 reflection from AlN crystal with evaporated substrate. Ww= 114 arcsec., W2q–w = 110 arcsec. Approximation of peaks by Gaussian and Voigt functions is shown with dashed and solid lines, respectively

a)

b)

Fig. 3. The scheme of possible mechanisms of misfit stress relaxation when growing the single crystal AlN layer on the evaporating SiC substrate. The initial relaxation stage due to nucleation of the moving dislocation half-loops on compressed AlN layer surface with thickness, much smaller than the thickness of the substrate (a). The final relaxation stage by the formation of L-shaped dislocation configurations in the AlN layer allowing for misfit stress relaxation both near and away from AlN/SiC  interface (b). The inserts schematically show misfit stress diagrams in the cross section of the structure and pyramidal slip plane in AlN layer

 

a)

b)

c)

 

d)

e)

 Fig. 4. A theoretical model of L-shaped dislocation configuration appearance near AlN/SiC interface. The initial state of plane coherent AlN layer with thickness h much less than the thickness of SiC substrate (a). The nucleation of a dislocation half-loop with Burger's vector b1, moving along pyramidal slip plane in the direction from AlN layer surface to AlN/SiC interface at h=hc (b). Surface step becomes overgrown and changes its face on mirror-symmetric one with h=h1>hc; the tilted line segment of b1-dislocation becomes overgrown from this face to AlN/SiC interface. The dashed line shows the position of AlN layer surface for h=hc (c). On the surface step "secondary" dislocation half-loop is nucleated with Burger's vector b2, and it slides symmetrically relative to b1-dislocation half-loop from AlN layer surface to AlN/SiC  interface at h=h2>h1. As a result, the surface step disappears, and L-shaped dislocation configuration begins to be formed. The dashed lines show the locations of AlN layer surface for h=hcand  h=h1 (d). End L-shaped dislocation configuration with an upper dislocation segment with Burger's vector b3=-b1-b2 and closing half-loops of b1 - and b2-dislocations, with  h=h3>h2 (e)



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