Defect analysis in AlGaN layers on AlN templates obtained by epitaxial lateral overgrowth
A. Mogilatenkoa,b , V. Küllera, A. Knauera, J. Jeschkea, U. Zeimera, M. Weyersa, G. Tränklea
Published in:
J. Cryst. Growth, vol. 402, pp. 222-229 (2014).
Abstract:
The defect distribution in thick AlN layers obtained by epitaxial lateral overgrowth (ELO-AlN) has been analyzed as a function of the miscut direction of the patterned sapphire substrate. A 0.25° miscut toward the sapphire a-plane leads to formation of smooth ELO-AlN layers containing vertical coalescence grain boundaries and exhibiting an almost homogeneous threading dislocation (TD) distribution with a TD density ranging from 5 × 108 cm-2 to 8 × 108 cm-2. In contrast, a 0.25° miscut toward the sapphire m-plane results in formation of periodically arranged macrosteps on the surface of the coalesced ELO-AlN layers as well as formation of inclined coalescence grain boundaries leading to an inhomogeneous TD distribution. A subsequent AlxGa1-xN deposition onto ELO-AlN template with surface macrosteps leads to Ga enrichment on the step sidewalls and, for lower Al-contents (e.g. x=0.5), even to additional defect formation. For higher Al contents (e.g. x=0.8) no additional threading dislocations are formed in the AlGaN layers and the observed TD density corresponds to that of the ELO-AlN template: less than 108 cm-2 in the wing regions and from 6 × 108 cm-2 to 9 × 108 cm-2 above the ridges. Compressive strain during growth of Al0.8Ga0.2N on ELO-AlN tends to be compensated by threading dislocation inclination. However, due to the low TD densities the inclination angles are more than 3 times larger than those observed in Al0.8Ga0.2N layers on planar AlN/sapphire templates.
a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
b Humboldt Universität zu Berlin, Institut für Physik, Berlin, Germany
Keywords:
A1. Crystal structure; A1. Defects; A3. Metal-organic vapor phase epitaxy; B1. Nitrides; B2. Semiconducting III-V materials.
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