Nano-indentation was used to investigate the plastic behaviour of a short-period superlattice. The sample was grown, onto a (001) surface of a GaAs single crystal, by means of metal-organic vapour-phase epitaxy. The mechanical response of the superlattice to nano-indentation testing was compared with that of a bulk GaAs (001) surface. Pop-in events were detected during indentation-loading, thus confirming that the superlattice structure contained a low defect density. The indentations were observed using transmission electron microscopy, and the plastic zone size which was associated with each indentation was measured as a function of the maximum load. The dislocation arrangements which were generated by indentation were analysed and were compared with the arrangements which were observed in deformed bulk GaAs. No stacking faults were observed in the plastic zone. At the edge of the plastic zone, perfect dislocations of 2 types were observed. Perfect dislocation lines extended in their Burgers-vector direction; parallel to the sample surface. A bowing at the end of the lines was observed which changed the screw character of the dislocation to 60º. The dislocations of the second group had a Burgers vector which was inclined to the surface, and formed loops which looked like butterfly wings in plan. These loops interacted with the 2-dimensional structure of the superlattice, and developed along 2 straight segments parallel to the structure. A super-Peierls effect was suggested to be responsible for strengthening of the superlattice.

Plastic Behaviour of an AlAs/GaAs Superlattice with a Short Period. E.Le Bourhis, G.Patriarche: Philosophical Magazine Letters, 2001, 81[4], 223-31