Crack-free Al0.45Ga0.55N epilayers, with and without graded-AlxGa1− xN/AlN multi-buffer layers, were grown onto AlN/sapphire templates using radio-frequency assisted molecular beam epitaxy. A significant reduction in dislocation content was achieved in the Al0.45Ga0.55N epilayer by using graded-Alx Ga1− xN/AlN multi-buffer layers. Transmission electron microscopy and Raman spectroscopy revealed that the compressive strain in the Al0.45Ga0.55N epilayer was effectively relaxed by the inclination of edge threading dislocations.

Relaxation of Compressive Strain by Inclining Threading Dislocations in Al0.45Ga0.55N Epilayer Grown on AlN/Sapphire Templates using Graded-AlxGa1−xN/AlN Multi-Buffer Layers. Q.M.Fu, T.Peng, F.Mei, Y.Pan, L.Liao, C.Liu: Journal of Physics D, 2009, 42[3], 035311