Different epitaxial structures have been studied by high-resolution x-ray diffraction and x-ray topography, Transmission Electron Microscopy and Atomic Force Microscopy to establish correlations between epitaxial growth conditions and crystal perfection. It was confirmed that epitaxial growth under initial elastic stress inevitably leads to the creation of extended crystal defects like dislocation loops and edge dislocations in the volume of epitaxial structures, which strongly affect crystal perfection and physical properties of future devices. It was found that the type of created defects, their density and spatial distribution strongly depended on growth conditions: 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 the volume density of extended defects as a parameter. It was found that the accommodation and relaxation of initial elastic stress and creation of crystal defect were up to four stages "chain" processes, necessary to stabilize the crystal structure at a level corresponding to the deterioration power of particular growth conditions.