We studied the structural and optical properties of high Al-content AlInGaN epilayers with different thicknesses grown on GaN/sapphire templates by metalorganic chemical vapor deposition (MOCVD). Direct evidences of the gradual evolution of the content of Al, Ga and In along the growth direction were obtained. When the film thickness was over a certain value, however, the AlInGaN epilayer with constant element contents began to form. These results were also supported by the blue shift and splitting of the photoluminescence (PL) peak. For the thinnest epilayer, the surface was featured with outcrops of threading dislocations (TDs) which suggested a spiral growth mode. With increase in thickness, step-flow growth mode and V-shaped pits were observed, and the steps terminated at the pits. (C) 2008 Elsevier B. V. All rights reserved.