Defect analysis in AlGaN layers on AIN templates obtained by epitaxial lateral overgrowth

The defect distribution in thick AIN layers obtained by epitaxial lateral overgrowth (ELO-AIN) has been analyzed as a function of the miscut direction of the patterned sapphire substrate. A 0.25 degrees miscut toward the sapphire -plane leads to formation of smooth ELO-A1N layers containing vertical coalescence grain boundaries and exhibiting an almost homogeneous threading dislocation (TD) distribution with a TD density ranging from 5 x 10(8) cm(-2) to 8 x 10(8) cm(-2). In contrast, a 0.25 degrees miscut toward the sapphire ra-plane results in formation of periodically arranged macrosteps on the surface of the coalesced ELO-AIN layers as well as formation of inclined coalescence grain boundaries leading to an inhomogeneous TD distribution. A subsequent Al0.8Ga0.2N deposition onto ELO-AIN 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-AIN template: less than 10(8) cm (2) in the wing regions and from 6 x 10(8) cm 2 to 9 x 10(8) cm(2) above the ridges. Compressive strain during growth of Al0.8Ga0.2N on ELO-AIN 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 AIN/sapphire templates. (C) 2014 Elsevier By. All rights reserved