[en] Ion implantation is being explored as a means of doping GaAs, with several potential applications to microwave and optoelectronic devices. In Research Department Report No. 611 results were presented of electrical measurements on epitaxial GaAs implanted with ion combinations classified as 'non-doping' (Ga, As or matched Ga + As), or 'doping' (Se, Ga + Se, or As + Se). The doses were 2 x 10¹⁴ cm^-2 of each ion at an implantation temperature of 200⁰C; subsequent annealing was at a temperature of 700⁰C. The subject of the present Report is a transmission electron microscopy (TEM) examination of similar specimens. Clear and reproducible differences were found in the dislocation loop size and density depending on the ion species implanted. Detailed consideration of the individual trends suggested that at higher annealing temperatures the electrical activity of 'stoichiometric' matched dual implants of Ga + Se (11% at 700⁰C) would be expected to show a greater margin of improvement on that of single implants of Se (7% at 700⁰C). (author)