The strain states induced by a lattice mismatch in epitaxial systems have been studied by Transmission Electron Microscopy (TEM) using the moire fringe technique on plane view samples. For the GaSb/(001)GaAs system, moire patterns suggest that the GaSb layer is free of stress and homogeneously relaxed by a perfect square array of Lomer dislocations. A 10 nm thick layer of GaInAs (20% In concentration) grown on (001)GaAs does not give any moire fringes for all low-index Bragg reflections: this result indicates that the effective misfit strain does not correspond to the theoretical one described by the elastic theory. Segregation effects are expected to play an important role in the relaxation of the misfit strain.
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