It has been found that AlGaN layers grown by MOCVD on sapphire substrates form superlattice (SL) along growth direction. Transmission electron microscopy (TEM), high resolution X-ray diffraction and atomic force microscopy (AFM) found the phenomenon. The amount of Al in AlGaN layer oscillates between a few percent to about 50%, thus by about one order of magnitude. The period of oscillations range from 30 nm to 50 nm depending on the growth condition. TEM and AFM reveal a homogenous lateral distribution of the SL. The vertical extension covers the total layer thickness.
It has been found that the appearance of SL depends on the thickness of the buffer layer on which the growth of AlGaN layer is initiated. The thinner buffer layer leads to the uniform growth of AlGaN layer without oscillating character. On the other hand the thicker buffer layer stimulate the oscillating growth, which persist throughout the whole growth process. The possible mechanism indicating oscillating character of reactions taking place on the surface of the grown AlGaN layer will be discussed.

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