Formation of misfit dislocations in thin film heterostructures

We have studied characteristics of 60degrees and 90degrees dislocations in GaAs/Si(100) thin-film heterostructures grown by metal-organic chemical-vapor deposition at 650 degreesC. The misfit dislocation network consists of approximately 60% of 90degrees dislocations, and 40% of the closely spaced pairs of 60degrees dislocations with intersecting glide planes. This ratio has remained essentially constant after rapid thermal annealing at 800 degreesC for 90 sec. It is envisaged that these 60degrees dislocation pairs have parallel screw components and as a result they cannot combine to form a 90degrees dislocation. Upon annealing, some of the 60degrees 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 60degrees dislocations is generated from the undulated surface above a critical thickness. The second set of 60degrees 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 60degrees dislocations caused by the interaction with the existing misfit dislocations. (C) 2002 American Institute of Physics.