Structural investigations of SiGe epitaxial layers grown by molecular beam epitaxy on Si(0 0 1) and Ge(0 0 1) substrates: I - High-resolution x-ray diffraction and x-ray topography

Epitaxial structures of different SiGe composition grown by molecular beam epitaxy on Si(0 0 1) and Ge(0 0 1) substrates have been studied by high-resolution x-ray diffraction and x-ray topography to establish correlations between epitaxial growth conditions and crystal perfection. It was confirmed that epitaxy under initial elastic stress inevitably led to the creation of extended crystal defects. The type of defects created and their density and spatial distribution, strongly depended on the value and sign of the initial elastic strain, the elastic constants of solid solutions, the temperature of deposition and growth rate, and the thickness of the epitaxial layers. All of the investigated structures were classified by their crystal perfection, using x-ray diffraction with the volume density of dislocation loops as a parameter. It was found that the accommodation and relaxation of initial elastic stress and creation of crystal defects were multistage "chain" processes, necessary to stabilize the crystal structure at a level corresponding to the particular growth conditions. Types, density and spatial distribution of crystal defects, related to each stage of defect creation and matched to structural features, as revealed by high resolution x-ray diffraction, were considered for explanation.