Effectiveness of non-linear graded buffers for In(Ga,Al)As metamorphic layers grown on GaAs (0Â 0Â 1)

We investigated the effectiveness of non-linear graded buffers for metamorphic In(Ga,Al)As layers grown on GaAs (0 0 1). The metamorphic In(Ga,Al)As layers with three types of graded buffers were grown on semi-insulating GaAs (0 0 1) 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 108 cm−2, which are insensitive densities in changing the electron transport properties in the heterostructures.