. Investigation by synchrotron radiation X­ray topography of lattice deformation in InGaAs/GaAs compositionally graded buffer layers

The synchrotron radiation plane wave topography and the Rutherford backscattering technique have been used to investigate the lattice tilts between substrates and layers introduced by the preferential orientation of the Burgers vectors of the misfit dislocations in compositionally graded InGaAs/GaAs heterostructures. A monotonic change of the lattice tilt along the sample surface producing in average a concave curvature of the buffer layer lattice has been found with a nearly complete alignment of the Burgers vector of the misfit dislocations at the sample edges. The topographic observations showed that the buffer layers can follow a nearly continuous curvature or can be sub-divided in large domains with different average lattice tilt. The models recently proposed for the formation of tilt in partially released structures are not able to explain the present observation of a lattice tilt varying coherently along the sample surface.