We report the structural characterization of the 3-D relaxation morphology of In0.4Ga0.6As grown on a step-graded InxGa1-xAs buffer layer on GaAs. Scanning electron microscopy showed “grooves” spaced on the order of microns running only in the  direction. Each groove was observed with cross-sectional transmission electron microscopy to mark the location of a vertical low-angle tilt and/or twist boundary. The veiy rough layer morphology may be the result of island coalescence or severe surface roughness that created the grain boudnaries as the layer grew. Strain relaxation in the In0.4Ga0.6As layer was much reduced in the  in-plane direction. The asymmetry in residual in-plane strains in the In0.3Ga0.7AS layer and/or the increased In composition may be responsible for the development of an anisotropic surface roughness. X-ray microanalysis revealed a periodic variation in layer composition which correlated with a fine contrast modulation presumably the result of phase segregation.
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