High quality AlGaN grown on ELO AlN/sapphire templates

• Miscut and etch depth of AlN/sapphire templates play an important role for surface morphology and TDD of thick ELO AlN.
• Surface steps on ELO AlN give rise to periodic Al inhomogeneities in subsequently grown AlxGa1−xN.
• Conditions for growth of high quality AlxGa1−xN layers on ELO AlN could be identified.
• Al0.8Ga0.2N with a homogeneous Al distribution and a TDD as low as 4.5×108 cm−3 was obtained.

The defect structure and the homogeneity of 1–3 µm thick AlxGa1−xN layers grown on epitaxially laterally overgrown (ELO) AlN on patterned AlN/sapphire templates have been investigated in dependence on the miscut direction of the c-plane sapphire substrates, the etching depth into the sapphire and the Al concentration. It was found that shallowly etched AlN/sapphire templates with a 0.25° miscut toward the a-plane provide a smooth surface of ELO AlN and therefore a good Al homogeneity in the overgrown Al0.8Ga0.2N layer. The threading dislocation density in these layers is as low as 5×108 cm−2.