Interpretation of the diffraction profile resulting from strain relaxation in epilayers

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Abstract
We have studied the profiles of the Bragg peaks and diffuse scattering in reciprocal space along both the plane perpendicular (qperpendicular to ) and plane parallel (q/sub ///) directions for sample structures consisting of layers of In0.1Ga0.9As grown by molecular beam epitaxy on (001) oriented GaAs substrates. The samples have different layer thicknesses and different dislocation distributions. We have measured the dislocation distributions in the interfaces using plan view transmission electron microscopy. We find that, for thin layers with low dislocation densities, the diffraction profiles in both the plane perpendicular (qperpendicular to ) and plane parallel (q/sub ///) can be modelled by considering two components of the diffraction profile, namely, dynamical scattering from the coherently coupled regions of perfect layer between dislocations and diffuse scattering from decoupled regions around the dislocations. From the q/sub /// profile a lateral dimension can be associated with the regions that give rise to the diffuse scattering, and we show that this dimension scales with the layer thickness. For thicker layers with higher dislocation densities, the strain fields of the dislocations overlap. In this case the diffraction profiles in (qperpendicular to ) are modelled by considering the ratio of the depth of coherently scattering decoupled crystal, above the dislocation array, with the total depth of the layer, assuming that scattering from the greatly distorted crystal close to the array is lost. Along q/sub /// the diffuse scattering is discussed on the basis of a statistical distribution of finite correlation lengths and microscopic tilts.