We investigated the effectiveness of non-linear graded buffers for metamorphic In(Ga,Al)As layers grown on GaAs (001). The metamorphic In(Ga,Al)As layers with three types of graded buffers were grown on semi-insulating GaAs (001) Substrates by means of molecular beam epitaxy. Materials were characterized by using atomic force microscopy, transmission electron microscopy, X-ray diffraction, Hall measurement, and photoluminescence. We found a tendency that the convex type is effective in enhancing optical and electron transport properties of the InGaAs metamorphic layers on GaAs. This can be attributed to alloy-hardening gradient of the graded buffers and different pair-annihilation probability in the InGaAs metamorphic layers. Electron transport properties with regard to the InGaAs/InAlAs metamorphic high electron mobility heterostructures on GaAs are independent on the types of graded buffers; near-surface threading dislocation densities of the graded buffers are on the order of 10(8) cm (2), which are insensitive densities in changing the electron transport properties in the heterostructures. (C) 2008 Elsevier B.V. All rights reserved.