Determination of Sapphire Off-Cut and Its Influence on the Morphology and Local Defect Distribution in Epitaxially Laterally Overgrown AlN for Optically Pumped UVC Lasers
J. Enslin1, A. Knauer2, A. Mogilatenko2, F. Mehnke1, M. Martens1, C. Kuhn1, T. Wernicke1, M. Weyers2, and M. Kneissl1,2
Published in:
phys. stat. sol. (a), vol. 216, no. 24, pp. 1900682 (2019).
Abstract:
Herein, a systematic study of the morphology and local defect distribution in epitaxially laterally overgrown (ELO) AlN on c-plane sapphire substrates with different off-cut angles ranging from 0.08° to 0.23° is presented. Precise measurements of the off-cut angle α, using a combination of optical alignment and X-ray diffraction with an accuracy of ±5° for the off-cut direction and ±0.015° for the off-cut angle, are carried out. For ELO AlN growth, a transition from stepflow growth at α<0.14° with height undulations on the surface to step bunching with step heights up to 20 nm for α>0.14° is observed. Furthermore, the terraces of the step-bunched surface exhibit curved steps. An analysis of the local defect distribution by scanning transmission electron microscopy and a comparison with atomic force microscopy reveal a bunching of defects in line with the ELO pattern and a roughening of step edges in highly defective regions. In addition, a reduction in the threshold excitation power density for optically pumped ultraviolet-C (UVC) lasers with smooth surface morphologies is observed.
1 Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, EW 6-1, 10623 Berlin, Germany
2 Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin, Germany
Keywords:
AlN, epitaxially laterally overgrown, off-cut, optically pumped lasers, sapphires, UVC.
Copyright © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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