  The strain of GaN layers grown by Metal Organic Chemical Vapor Deposition
(MOCVD) on three vicinal 4H-SiC substrates (0, 3.4 and 8 offcut from [0001]
towards [11-20] axis) is investigated by X-ray Diffraction (XRD), Raman
Scattering and Cathodoluminescence (CL). The strain relaxation mechanisms are
analyzed for each miscut angle. At a microscopic scale, the GaN layer grown on
on-axis substrate has a slight and homogeneous tensile in-plane stress due to a
uniform distribution of threading dislocations over the whole surface. The GaN
layers grown on miscut substrates presented cracks, separating areas which have
a stronger tensile in-plane stress but a more elastic strain. The plastic
relaxation mechanisms involved in these layers are attributed to the step flow
growth on misoriented surfaces (dislocations and stacking faults) and to the
macroscopical plastic release of additional thermoelastic stress upon cooling
down (cracks).
