Spontaneous compositional modulation in the AlGaN layers of a thick AlGaN/GaN multilayer structure

A periodic modulation with the wave vector parallel to the [0001] direction was observed in the AlGaN layers of a thick AlGaN/GaN multilayer heterostructure grown by metalorganic chemical vapor deposition. The modulation was attributed to a nearly sinusoidal spatial variation of the Al/Ga ratio with an average periodicity of about 3 nm. The observed periodicity was highly regular and incommensurate with the periodicity of the underlying lattice. The average Al fraction in the AlxGa1−xN layers was estimated to be x=0.115±0.010 and the peak-to-valley amplitude of the modulation was estimated to be Δx=0.075±0.016.