EFFECTS OF GAAS SUBSTRATE MISORIENTATION ON STRAIN RELAXATION IN INXGA1-XAS FILMS AND MULTILAYERS

We have investigated the effects of GaAs substrate misorientation on s train relaxation in InxGa1-xAs films and multilayers. Our calculations of shear stresses due to misfit strain, resolved on the glide plane i n the glide direction, reveal that the alpha and beta 60 degrees slip systems are influenced in a nearly identical fashion, for all substrat e misorientation directions. Thus, classical models for nucleation and glide of 60 degrees dislocations predict that a substrate misorientat ion will not influence the degree of [110] asymmetry in strain relaxat ion in lattice-mismatched zincblende semiconductor films. Contrary to these predictions, our experimental results reveal asymmetries in stra in 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 easi ly explained by differences in the intrinsic core properties of alpha and beta dislocations. Furthermore, in fully relaxed multilayers (grow n at lower temperatures), and single layers (grown at higher temperatu res), epilayer tilt which increases the (111)B substrate miscut is obs erved. In the multilayers, this behavior is found to be correlated wit h the presence of micron-scale surface facets. We consider possible ex planations for these results, including nucleation of partial dislocat ions, interaction of gliding threading dislocations, and strain relaxa tion predominated by forward and backward gliding cu threading disloca tion segments. Together, these results support the conclusion that loc al surface or interface step morphologies are more important than bulk stress effects in determining misfit dislocation formation in the InG aAs/GaAs system. (C) 1998 American Institute of Physics.