The Evolution of Strain Relaxation Close to The Critical Thickness
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ABSTRACT High resolution X-ray diffraction space mapping has been used to follow the change in the distribution of residual strain and localised relaxation in low mismatched epitaxial layers. Using this new technique, we have obtained a series of diffraction space maps of partially relaxed epitaxial layers of In.,GaA•,s on GaAs. The layers have different thicknesses and hence different degrees of strain relaxation. The diffuse scatter close to the Bragg peaks provides information about the imperfect and distorted regions in the structure and this has allowed us to examine the extent and distribution of residual strain close to the dislocations. We have followed the evolution of local relaxation, which is confined initially to regions around isolated dislocations, through to the case of overlapping dislocation strain fields, leading to a more homogeneous strain field distribution and microscopic and macroscopic tilting of the layers. INTRODUCTION An understanding of the processes involved in mismatch strain relaxation, in pseudomorphic layers, is vital for the successful prediction of residual strain in relaxed layers. To be able to predict the residual strain of a buffer layer structure is a necessary skill for the systematic design and development of relaxed Buffer Layers for semiconductor device technology1 ',. In the III-V low mismatch (
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