INVESTIGATION OF CRYSTAL DEFECTS IN III-V HETEROSTRUCTURES BY X-RAY TOPOGRAPHY AND ELECTRON-MICROSCOPY

III-V heteroepitaxial structures are often affected by the presence of typical extended crystal defects that have detrimental effects on the devices performances. Since layers and substrate have the same crystal structure, but different lattice parameters, the accommodation at the interface may occur either by elastic deformation of the layer unit cell or by the formation of misfit dislocations parallel to the interface itself. Several experimental findings concerning the strain relaxation mechanisms, the spatial distribution and the nature of the misfit dislocations are reported and discussed. In addition to the misfit dislocations, other extended crystal defects may be present within the epilayers; experimental results on threading dislocations, microcracks, twins and stacking faults, both single and arranged in tetrahedral pyramids, are reported.