STRAIN RELAXATION IN COMPOSITIONALLY GRADED INGAAS GAAS HETEROSTRUCTURES/

Epilayer strain relaxation in the InGaAs/GaAs system occurs via two me chanisms, plastic deformation and/or surface roughening. Under conditi ons of two-dimensional growth, we find that compositionally graded InG aAs/GaAs (001) multi-layer buffer structures will plastically deform w ith <110> misfit dislocations approaching 100% strain relaxation. At h igher growth temperatures, large-amplitude toughening is observed pref erentially along the [110] direction, and the strain relaxation become s asymmetric in the <110> directions. In single epilayers, the symmetr y of the strain relaxation is dependent on the magnitude of the substr ate offcut angle. In all cases, the epilayers develop a tilt about an in-plane axis in proportion to and opposite in direction to the substr ate offcut. With roughening, there is also a change in the orientation of the tilt axis such that only the dislocations with [1(1) over bar0 $] line directions develop a preferred tilt component. These results i llustrate the importance of surface steps and morphologies to strain r elaxation and perhaps offer clues to the identification of the disloca tion formation mechanisms at these interfaces.