Increasing the periodicity and total thickness of the MQWs revealed a cumulative deteriorating effect. The intersection of already created DLs for continued MQW growth increased the number of edge G007-LK created at substrate/epi-structure interface and in the volume of the MQWs. The former led to the onset of relaxation of initial elastic stress, while the latter led to deterioration of the spatial coherence.
Three distinct stages of defect creation were obtained by varying the MQW period. While a diminished thickness of the QW layers (4+8 nm structure) revealed primary DLs as the main type of deterioration, the 8+16 nm structure led to enhanced creation of secondary DLs representing the succeeding deterioration stage. Closing-edge segments were formed at a density on the substrate/MQW interface not sufficient for noticeable stress relaxation. The 8+8 nm structure represented an even more advanced stage of defect creation in which the creation of tertiary DLs on the interface, and most importantly, their intersection in the volume of MQW and the location of closing-edge segments close to epitaxial interfaces were sufficient to initiate relaxation of elastic stress.