GaAsP buffer layers grown on (001) just oriented GaP substrate show an undulated vicinal surface morphology and a thickness modulated GaAs/GaAsP strained superlattice layer grew on the vicinal GaAsP buffer layer. Structural characteristics of the thickness modulated superlattice have been carried out by transmission electron microscopy (TEM). In the thickness modulated structure, the first GaAs layer grown on the vicinal GaAsP buffer layer consisted of (001) and (117) facets, and thicker GaAsP grew on thinner GaAs and vice versa. Nano-beam electron diffraction revealed that an inhomogeneous residual strain distribution existed in the first GaAs layer. Therefore, the value of strain introduced in subsequent superlattice layers should be different from place to place and the strains in GaAs and GaAsP superlattice layers are also different from each other. The nucleus formation rate is inversely proportional to the value of the strain. So it is understood that the strain distribution in the first GaAs layer results in the successive thickness modulation of GaAs/GaAsP superlattice layers. (C) 2012 Elsevier B.V. All rights reserved.