The defect contents of small GaAs islands that had been grown, by means of molecular beam epitaxy, onto an (001) Si substrate were investigated by means of high-resolution electron microscopy. It was found that the smallest islands that were not defect-free contained stair-rod dislocations, with Burgers vectors of 1/6[11¯0] or 1/3[11¯0], that were linked to intrinsic or extrinsic stacking faults. When 2 stair-rod dislocations were present at the same time, they could interact to form an ultra-thin twin in GaAs. A triple-line intrinsic stacking fault/nano-twin/extrinsic stacking fault could then form, along which an edge 1/3[001¯] dislocation was present. A mechanism was proposed, for the triple node, that was based upon the formation of planar defects which were produced by emission from the free surface.

M.Loubradou, R.Bonnet, A.Vilà: Philosophical Magazine Letters, 1996, 74[1], 1-8