AbstractMolecular ion S2+ and SiFn+ implantations into GaAs have been investigated to form very thin active layers. After implantation, the transient annealing (TA) and furnace annealing (FA) were used. The measurements of activation efficiency, mobility, carrier concentration profiles and PL spectra were carried out. The experiments show that after TA, the activation efficiency, mobility and carrier distribution are almost the same between samples implanted with S+ at an energy of 50KeV to a dose of 3×1013cm−2 and S+2 at 100KeV to 1.5×1013cm−2. It shows that the damage of S2-implanted samples can be removed by TA, and a very thin active layer can be formed by the implantation of S2+ at 50KeV. For SiFn-implanted samples, the activation efficiency and mobility. decrease with increase of the implanted ion mass. As+ co-implantation into SiF-implanted samples has been used to improve both activation efficiency and mobility. After comparison with the properties of the SiFt implantation, S2+implantation is more acceptable to form thin active layers.