AlN overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy

S. Waldea, S. Hagedorna, P.-M. Coulonb,c, A. Mogilatenkoa, C. Netzela, J. Weinricha, N. Susilod, E. Zifferd, L. Matiwee, C. Hartmanne, G. Kuschf, A. Alasmarif, G. Naresh-Kumarf, C. Trager-Cowanf, T. Wernicked, T. Straubingere, M. Bickermanne, R.W. Martinf, P.A. Shieldsb,c, M. Kneissla,d, M. Weyersa

Published in:

J. Cryst. Growth, vol. 531, pp. 125343 (2020).

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Abstract:

We present overgrowth of nano-patterned sapphire with different offcut angles by metalorganic vapor phase epitaxy. Hexagonal arrays of nano-pillars were prepared via Displacement Talbot Lithography and dry-etching. 6.6 µm crack-free and fully coalesced AlN was grown on such substrates. Extended defect analysis comparing X-ray diffraction, electron channeling contrast imaging and selective defect etching revealed a threading dislocation density of about 109cm-2. However, for c-plane sapphire offcut of 0.2° towards m direction the AlN surface shows step bunches with a height of 10 nm. The detrimental impact of these step bunches on subsequently grown AlGaN multi-quantum-wells is investigated by cathodoluminescence and transmission electron microscopy. By reducing the sapphire offcut to 0.1° the formation of step bunches is successfully suppressed. On top of such a sample an AlGaN-based UVC LED heterostructure is realized emitting at 265 nm and showing an emission power of 0.81 mW at 20 mA (corresponds to an external quantum efficiency of 0.86%).

a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany
b Centre of Nanoscience & Nanotechnology, University of Bath, Bath BA2 7AY, UK
c Department of Electronic and Electrical Engineering, University of Bath, Bath BA2 7AY, UK
d Institute of Solid State Physics, Technical University Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
e Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin, Germany
f Department of Physics, SUPA, University of Strathclyde, 107 Rottenrow East, Glasgow G4 0NG, UK

Keywords:

A3. Metal organic vapor phase epitaxy; B1. Nitrides; B1. Sapphire; B3. Light emitting diodes