REARRANGEMENT OF MISFIT DISLOCATIONS IN GAAS ON SI BY POSTGROWTH ANNEALING

The effects of post-growth annealing have been investigated on the mov ement and rearrangement of two different groups of misfit dislocations in molecular beam epitaxially grown GaAs on tilted (3 degrees toward [110]) Si(001) substrates by using transmission electron microscope. T he group I misfit dislocations show a cross-grid structure running alo ng two [110] directions at the interface and are already formed in sma ll islands of 20-30 nm in size. The spacing of similar to 9.5 nm betwe en the dislocations along each [110] is constant throughout all of the growth stages from 10 nm to 3 mu m in GaAs thickness, although the cr oss grid pattern becomes more clear and regular due to annealing treat ment. On the other hand, the group II misfit dislocations show short a nd segmented structures approximately along the [110] directions, whic h we consider to be related to threading dislocations. They are very m obile, and gradually become rearranged with the extension of their len gth along the [110] directions near to the interface, as the annealing temperature increases. The group I and II misfit dislocations are tho ught to be generated due to stresses caused by the lattice misfit and the thermal expansion misfit between GaAs and Si, respectively.