Peculiarities of extended defect system in III-nitrides with different degrees of order of mosaic structure

Extended defect system (EDS), which included the threading dislocations and the mosaic structure in GaN epilayers grown on (0 0 0 1) sapphire substrates by MOCVD, has been investigated by transmission electron microscopy and atomic force microscopy. Strain relaxation of EDS with different degrees of order of mosaic structure (DOMS, Delta) has been found to distinguish noticeably. For EDS with poor DOMS (Deltagreater than or equal to0.34), a 3D-growth with a formation of large agglomerates of the mosaic structure domains in the regions near the threading (screw) dislocations has occurred. Numerous domain dislocation boundaries in these structures have been observed. Coherent concordance of domains with the formation of the dilatation boundaries was more typical of EDS with the better DOMS (Delta<0.34). Moreover, 2D-growth with the formation of additional growth steps with participation of screw dislocations has been observed. The optical and electrical properties of GaN epilayers correlate well with these structural peculiarities. (C) 2003 Elsevier B.V. All rights reserved.