Effects of GaAs substrate misorientation on strain relaxation in InxGa1−xAs films and multilayers

Abstract

We have investigated the effects of GaAs substrate misorientation on strain relaxation in InxGa1−xAs films and multilayers. Our calculations of shear stresses due to misfit strain, resolved on the glide plane in the glide direction, reveal that the α and β 60° slip systems are influenced in a nearly identical fashion, for all substrate misorientation directions. Thus, classical models for nucleation and glide of 60° dislocations predict that a substrate misorientation will not influence the degree of 〈110〉 asymmetry in strain relaxation in lattice-mismatched zincblende semiconductor films. Contrary to these predictions, our experimental results reveal asymmetries in strain relaxation (for partially relaxed single layers) which favor those dislocations aligned with the offcut axis. These asymmetries depend on the substrate misorientation and growth temperature, and are not easily explained by differences in the intrinsic core properties of α and β dislocations. Furthermore, in fully relaxed multilayers (grown at lower temperatures), and single layers (grown at higher temperatures), epilayer tilt which increases the (111)B substrate miscut is observed. In the multilayers, this behavior is found to be correlated with the presence of micron-scale surface facets. We consider possible explanations for these results, including nucleation of partial dislocations, interaction of gliding threading dislocations, and strain relaxation predominated by forward and backward gliding α threading dislocation segments. Together, these results support the conclusion that local surface or interface step morphologies are more important than bulk stress effects in determining misfit dislocation formation in the InGaAs/GaAs system.