It has been found that ion implantation doping results in the generation and diffusion of defect species, forming deep trapping levels. The effect of these levels on the electrical characteristics of zinc‐implanted GaAs diodes has been observed for the case of 70‐kV implantation at 400°C into substrates withn‐type concentrations ranging from 1 × 1016to 1.8 × 1018atoms/cm3. Capacitance‐voltage measurements have indicated the presence of a semi‐insulating layer in the diodes, varying in thickness from 0.18 &mgr; for the most heavily doped substrate to 2.7 &mgr; for the lightest. Frequency dependence of the junction capacitance and power law variation of forward current vs voltage have also been observed and are attributed to deep levels.