Unique x‐ray diffraction pattern at grazing incidence from misfit dislocations in SiGe thin films

Grazing‐incidence x‐ray diffraction (GIXD) permits the direct measurement of in‐plane lattice parameters of SiGe films that are too thin to yield good results from normal‐geometry triple‐axis techniques. A unique ‘‘X’’‐shaped pattern has been seen in H–K reciprocal space maps of diffracted x‐ray intensity from SiGe films that have relaxed via a modified Frank–Read mechanism. Contours of intensity are seen along the 〈110〉 directions from the (400) reciprocal lattice peak with the introduction of the first dislocations. For higher dislocation densities the X‐shaped contours are anisotropically distorted and a satellite peak, corresponding to the lattice parameter for a partially relaxed film, becomes identifiable at lower H. In contrast, H–K reciprocal‐space contours from thin SiGe films that have relaxed by roughening and subsequent random nucleation of dislocations display broad, oval‐shaped contours centered at the (400) reciprocal lattice point for the film. Numeric simulations of GIXD from a variety ...