The formation of crystalline defects is studied as a function of the epitaxial layer thickness in InGaAs and GaAsSb material systems grown by molecular beam epitaxy on (001) GaAs wafers. The Sb and In composition is roughly 8% in both sets of samples while the nominal thicknesses are respectively 50, 125, 250nm and 500nm for the InGaAs structures and 100, 250 and 500nm for the GaAsSb structures. High-resolution x-ray diffraction results show that similar partial relaxation is obtained in both systems for nearly the same thickness. Consistent structural transformation of point defects into dislocation loops related to the thickness of ternary layers is revealed. This resulted in a partial relaxation of 42 and 46% in the 250 nm thick GaAsSb and InGaAs layers respectively due to a density of secondary 60° dislocation loops of ∼ 1 × 109 cm-2. The relaxation increased to 64% in the 500nm thick InGaAs and to 68% for the 500nm thick GaAsSb films even though the density of 60° dislocation loops in the volume was reduced due to intersections of these dislocation loops. Explanation of revealed structural features is suggested.