Ultrafast optoelectronic characteristics of GaAs implanted with 200 keV arsenic ions at dosage as low as1013 ions/cm2are reported. Ultrashort photoexcited carrier lifetimes of0.23±0.02,0.87±0.02,and3±0.2 pswere determined for as-implanted, rapid thermal annealing (RTA) (600 °C for 30 s) and furnace-annealed (600 °C for 30 min) arsenic-ion-implanted GaAs orGaAs:As+,respectively. The switching response of photoconductive switches (PCSs) fabricated on the latter two materials were∼3and 8 ps, respectively. The leakage current of the PCS fabricated on furnace-annealed sample was as low as 30 nA. The breakdown fields exceeded 150 (instrument-limited) and 90 kV/cm for furnace- and RTA-annealed samples, respectively. The optical responsivity of low-dosage arsenic-implanted GaAs photoconductive switch can be as high as 0.01 A/W. This also compared favorably with the same device made on state-of-the-art photoconductor such as molecular-beam epitaxy grown GaAs at low temperatures. ©1997 American Institute of Physics.