Single crystaln-GaAs substrates have been implanted at room temperature with120Snions at an energy of 70 MeV. The optical microscope and scanning electron microscope studies of the cross section of the implanted samples have shown the formation of two sharp layers at a depth of 8.7 and 11 &mgr;m from the surface of the substrate. The electrical characteristics of the Schottky diodes fabricated on the implanted substrates at room temperature indicate the presence of high series resistance due to radiation defects. The electrical properties of the implanted samples were investigated after implantation and annealing to 850 °C. Low temperature resistance measurements of these samples indicate that the samples annealed to 450 °C are dominated by a variable range hopping conduction mechanism, whereas for the samples annealed at 550 and 650 °C the electrical conduction is due to hopping between the neighboring defect sites. At annealing temperatures higher than 650 °C, the electrical transport below room temperature seems to be dominated by carriers in the extended states, which are also responsible for the electrical conduction at room temperature and above, for the samples annealed at temperatures higher than 450 °C. ©1997 American Institute of Physics.