Semipolar GaN-based heterostructures on foreign substrates

This paper reviews our recent investigations about semipolar GaN-based optoelectronic heterostructures grown on foreign substrates. Two basically different approaches are discussed, both making use of epitaxial growth in the polar c-direction to minimize any crystalline defects. By selective area growth, stripes with triangular cross-section have been formed with semipolar side-facets, on which quantum well and electroluminescence test structures have been deposited. By careful optimisation of many growth parameters, we could drastically increase the growth temperature of GaInN quantum wells emitting beyond 500 nm. In the second approach, the GaN growth starts on inclined sapphire c-planes, which form the side facets of trenches etched into the substrates. After coalescence, planar semipolar GaN layers can be achieved. We investigated various sapphire wafer orientations leading to {1122}, {1011}, and {2021} layers. After careful optimisation with a major focus on the decrease of the stacking fault density, we have also investigated the doping behaviour of such semipolar structures. Eventually, full electroluminescence test structures could be grown. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim