Scanning Microscopy


Epilayer strain relaxation in the InGaAs/GaAs system occurs via two mechanisms, plastic deformation and/or surface roughening. Under conditions of two-dimensional growth, we find that compositionally graded InGaAs/GaAs (001) multi-layer buffer structures will plastically deform with < 110 > misfit dislocations approaching 100% strain relaxation. At higher growth temperatures, large-amplitude roughening is observed preferentially along the [110] direction, and the strain relaxation becomes asymmetric in the < 110 > directions. In single epilayers, the symmetry of the strain relaxation is dependent on the magnitude of the substrate offcut angle. In all cases, the epilayers develop a tilt about an in-plane axis in proportion to and opposite in direction to the substrate offcut. With roughening, there is also a change in the orientation of the tilt axis such that only the dislocations with [110] line directions develop a preferred tilt component. These results illustrate the importance of surface steps and morphologies to strain relaxation and perhaps offer clues to the identification of the dislocation formation mechanisms at these interfaces.

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