Homogeneous nucleation of dislocations in In0.4Ga0.6As/GaAs near critical thickness

Homogeneous nucleation of dislocation loops was observed in In0.4Ga0.6As/GaAs films grown with thicknesses near critical thickness (5 nm) for this system. In films with larger thicknesses the dislocation networks were observed as irregular orthogonal arrays. The irregular arrays presumably form from the dislocation loops that grow and interact as the In0.4Ga0.6As film thickens. These results are in sharp contrast to those obtained on films with x≤0.25. Here long dislocation segments are observed even in films with thicknesses just above critical value and the films with larger thicknesses exhibit a regular orthogonal array of dislocations. We attribute these differences in dislocation morphology between the low and high x-value material to a change in the nucleation mechanism for dislocation formation. This change, in turn, corresponds to an observed change from two-dimensional growth at lower x values to three-dimensional growth at higher values. The three-dimensional growth of In0.4Ga0.6As was confirmed by RHEED observations.