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 Deltax = 0.075 +/-0.016. (C) 2001 American Institute of Physics.