Influence of alloy composition and interlayer thickness on twist and tilt mosaic in Al_xGa_1-xN/AlN/GaN heterostructures

The effect of an AlN interlayer between micron thick GaN and Al _xGa_1-xN layers was investigated using high-resolution x-ray diffraction, in surface symmetric, skew symmetric, and grazing incidence in-plane diffraction geometrics. Growth of the epilayers was carried out using low pressure metalorganic vapor phase epitaxy in a showerhead reactor. An increase in twist mosaic, and thus threading edge dislocation density, with increased Al fraction was observed in the AlGaN layer. Increase of the Al content for a constant interlayer thickness decreased the lattice mismatch with respect to the AlN interlayer.