Characterisation by TEM and X-ray diffraction of linearly graded composition InGaAs buffer layers on (001) GaAs

The dislocation distribution in linearly graded composition layers of InGaA s on GaAs is studied by transmission electron microscopy (TEM). Dislocation s 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 o f dislocations in the substrate. The observed dislocation distribution in t he first region of the graded layer is compared to that predicted by severa l models. The differences between the models' predictions and observations reported here are discussed. The description of the strain relaxation mecha nism given by Dunstan's model is shown to give the best fit to the results reported in the present paper.