Formation of misfit dislocations in thin film heterostructures

We have studied characteristics of 60° and 90° dislocations in GaAs/Si(100) thin-film heterostructures grown by metal-organic chemical-vapor deposition at 650 °C. The misfit dislocation network consists of approximately 60% of 90° dislocations, and 40% of the closely spaced pairs of 60° dislocations with intersecting glide planes. This ratio has remained essentially constant after rapid thermal annealing at 800 °C for 90 sec. It is envisaged that these 60° dislocation pairs have parallel screw components and as a result they cannot combine to form a 90° dislocation. Upon annealing, some of the 60° dislocation pairs split to form stacking faults in agreement with our earlier model. Based upon these observations, we propose a model where a first set of 60° dislocations is generated from the undulated surface above a critical thickness. The second set of 60° dislocations is nucleated at a larger thickness and at the smoother surface. The Burgers vectors of these dislocations are controlled by the dislocations from the first set, and only low-energy dislocation pairs are formed through glide towards the interface and later through short glide and climb along the interface plane. We have used a numerical analysis based on elasticity theory to evaluate the changes in the nucleation barrier for the 60° dislocations caused by the interaction with the existing misfit dislocations.