Strain relaxation and crystallographic tilt of compositional graded InxGa1-xAs and InxAl1-xAs (0<x<0.3) epilayers grown on GaAs substrates

The strain relaxation and crystallographic tilt of InxGa1-xAs and InxAl1-xAs (0<x<0.3) epilayers grown on GaAs substrates have been studied. Compositional step-graded or linear-graded buffer layers are used. The residual strain of the InxAl1-xAs/graded InyAl1-yAs is found to be larger than that of InGaAs and is strongly dependent on the thickness and the composition of the step-graded buffer layers. The crystallographic tilt of the InGaAs epilayers with respect to GaAs substrate is shown to be strongly dependent on the substrate temperature as well as the layer structure of the underlying buffer layer, while that of InAlAs is insensitive to these two factors. Rough surface due to irregular nucleation is proposed to explain the different behavior between these two material systems.