It was recalled that Intrinsic stresses due to lattice mismatch, high densities of threading dislocations, and extrinsic stresses resulting from the mismatch in the coefficients of thermal expansion, were present in almost all III-nitride heterostructures. Stress relaxation in the GaN layers occurred in conventional, cantilever and in pendeo-epitaxial films via the formation of additional misfit dislocations, domain boundaries, elastic strain and wing tilt. Polychromatic X-ray micro-diffraction, high resolution monochromatic X-ray diffraction and scanning electron microscopic analysis were used to determine the crystallographic properties, misfit dislocations distribution and crystallographic tilts in uncoalesced GaN layers grown by using pendeo-epitaxial and cantilever methods. The crystallographic tilt between the GaN(00▪1) and Si(111) planes was detected in the cantilever-grown samples on Si(111). In contrast there was no tilt between GaN(00▪1) and SiC(00▪1) planes in pendeo-epitaxially grown samples. The wings were tilted upward for both the pendeo-epitaxial and cantilever grown uncoalesced GaN layers.

Characterization of Crystallographic Properties and Defects via X-Ray Microdiffraction in GaN (00▪1) Layers. R.I.Barabash, O.M.Barabash, G.E.Ice, C.Roder, S.Figge, S.Einfeldt, D.Hommel, T.M.Katona, J.S.Speck, S.P.DenBaars, R.F.Davis: Physica Status Solidi A, 2006, 203[1], 142-8