Electrical and dynamical optical characterization of As-ion implanted and annealed GaAs has been performed. Changes of physical properties induced by annealing have been studied in detail by using layers annealed in small steps in the temperature range 500-700 degrees C. The carrier trapping rate increases exponentially with increase of inverse annealing temperature indicating that in ion-implanted GaAs ultrafast carrier capture occurs to the same trapping centers as in low-temperature-grown GaAs. Relatively large resistivity and electron mobility in As-implanted GaAs have been observed after annealing, which shows that this material possesses properties required for a variety of ultrafast optoelectronic applications.