Correlation of sapphire off-cut and reduction of defect density in MOVPE grown AlN
A. Knauer1, A. Mogilatenko1, S. Hagedorn1, J. Enslin2, T. Wernicke2, M. Kneissl1,2, and M. Weyers1
Published in:
phys. stat. sol. (b), vol. 253, no. 5, pp. 809-813 (2016).
Abstract:
X-ray diffraction and TEM investigations of MOVPE grown AlN on sapphire with small off-cuts to a- and m-plane reveal the influence of the off-cut direction and angle on the reduction of threading dislocation density by annihilation during growth. Higher off-cut angles as well as off-cut to a-plane seem to facilitate the annihilation, with the main reduction taking place within the first 300 nm layer thickness. On planar substrate the thickness is limited by cracking to below 2 µm which also limits the ability to further reduce the defect density. By epitaxial lateral overgrowth on stripe patterned substrates the crack-free thickness is increased and further reduction of the defect density is possible. This process is effective up to 3-5 µm layer thickness. Using templates with off-cuts ≥0.28° to m-plane, step bunching perpendicular to the stripe direction occurs and bends the vertically directed threading dislocations into inclined grain boundaries starting from the point of coalescence. These partially block/incline threading dislocations over the ridge areas and thus further reduce the dislocation density. The dislocations are concentrated in stripes over the ridges and the coalescence areas. For smaller off-cut to m or especially for off-cut to a-plane, the dislocation distribution is more homogeneous but nevertheless stripe-like with alternating densities of low 108 cm-2 in the laterally overgrown areas and low 109 cm-2 in the areas over the ridges and the coalescence lines.
1 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, 12489 Berlin, Germany
2 Institute of Solid State Physics, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
Keywords:
AlN, MOCVD, MOVPE, sapphire, transmission electron microscopy, X-ray diffraction.
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