Strong correlations between crystal perfection of epitaxial structures and size, density and PL features of deposited InAs QDs have been found. Increase of a Sb composition in GaAsSb strain relief layers from 8% to 37% significantly disturbed crystal perfection of epitaxial structures and increased the density of deposited QDs from 2-2.5 × 10 10 cm -2 at 8% Sb structure to 7.5-9.5 × 10 10 cm -2 at 16% Sb structure. At 37% Sb initial elastic stress was noticeably relaxed (≈ 40%) while creation of QDs was fully blocked. Relaxation of elastic stress strongly increased the density of dislocation loops in epitaxial layers and affected atomic migration on the growth front. Observed correlations between density of dislocation loops and QDs are related with a diminution of the energy of migrated atoms, caused by dislocations. At definite density of dislocation loops, reduced energy diminished accumulation of deposited atoms below the level critical for their transformation to QDs.