Anisotropy lattice mismatch strains

These findings underline the strong impact of the crystal anisotropy on the dislocation-related stress in the films, which has to be considered for examples for the interpretation of X-ray diffraction patterns performed on these layers. It can be expected that the strong anisotropy of the lattice mismatch results in an anisotropic formation of defects for stress accommodation, thus leading to anisotropic strain fields. 

These results are consistent with those reported by Onojima et al. [27]- Two possible causes may account for the anisotropy of the a-plane nitride layers, namely (i) an anisotropy of the strain relaxation in the buffer coming from an in-plane anisotropy of the lattice mismatch between AlN and SiC (-1-1.0% along [1-100] and —1.2% along [0001]) and (ii) the presence of c-plane stacking faults propagating through the nitride layer and emerging at the surface of the buffer, which results in the observed ripples [20, 27]. 

The lattice and thermal mismatch between the substrate and the film, characteristic for the heteroepitaxial growth of the nitrides on foreign substrates, results in the presence of strain. This strain has a major effect on all fundamental material properties and device-relevant characteristics, and has been a subject of intense investigation. The strain in the nonpolar nitrides is supposed to be anisotropic owing to the in-plane anisotropies in the lattice matching and the thermal expansion coefficients of both the substrates and the layers along the ]0001] and [1-100] directions. 

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