INTERPRETATION OF THE DIFFRACTION PROFILE RESULTING FROM STRAIN RELAXATION IN EPILAYERS

We have studied the profiles of the Bragg peaks and diffuse scattering in reciprocal space along both the plane perpendicular (q(perpendicul ar to)) and plane parallel (q(parallel to)) directions for sample stru ctures consisting of layers of In0.1Ga0.9As grown by molecular beam ep itaxy on [001] oriented GaAs substrates. The samples have different la yer thicknesses and different dislocation distributions. We have measu red the dislocation distributions in the interfaces using plan view tr ansmission electron microscopy. We find that, for thin layers with low dislocation densities, the diffraction profiles in both the plane per pendicular (q(perpendicular to)) and plane parallel (q(l)) can be mode lled by considering two components of the diffraction profile, namely, dynamical scattering from the coherently coupled regions of perfect l ayer between dislocations and diffuse scattering from decoupled region s around the dislocations. From the q(parallel to) profile a lateral d imension can be associated with the regions that give rise to the diff use scattering, and we show that this dimension scales with the layer thickness. For thicker layers with higher dislocation densities, the s train fields of the dislocations overlap. In this case the diffraction profiles in (q(perpendicular to)) are modelled by considering the rat io of the depth of coherently scattering decoupled crystal, above the dislocation array, with the total depth of the layer, assuming that sc attering from the greatly distorted crystal close to the array is lost . Along q(parallel to) the diffuse scattering is discussed on the basi s of a statistical distribution of finite correlation lengths and micr oscopic tilts.