The dislocation distribution in linearly graded composition layers of InGaAs on GaAs is studied by transmission electron microscopy (TEM). Dislocations are shown to penetrate into the substrate and to invade the first part of the graded layer. A simple balance of forces model predicts the presence of dislocations in the substrate. The observed dislocation distribution in the first region of the graded layer is compared to that predicted by several models. The differences between the models’ predictions and observations reported here are discussed. The description of the strain relaxation mechanism given by Dunstan's model is shown to give the best fit to the results reported in the present paper.
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