Differently doped GaAs crystals were irradiated at 4 K with 0.4- and 2.2-MeV electrons and were investigated by optical absorption spectroscopy with special emphasis on the magnetic circular dichroism of the optical absorption (MCDA). The MCDA yields very characteristic fingerprints of two VGa-related defects and of the different arsenic antisites AsGa-X1, AsGa-X2, and EL2. Using these fingerprints the production and the thermally activated reactions of these defects were systematically investigated up to the final annealing at Ta~=850 K. We show that both sublattices are involved in the defect production even at the lowest electron energies and discuss the importance of replacement collisions. Many antisite defects survive the well-known annealing stages (I to III) of Frenkel pairs. EL2 defects seem to be the most stable antisite configuration and are also observed in n-type GaAs that contained no EL2 defects before irradiation. A comparison of the spectra obtained after low-temperature irradiations and annealing with spectra obtained after corresponding high-temperature irradiations shows remarkable similarities. All kinds of AsGa-related complexes are usually present simultaneously and we deduce a consistent picture of the visibility of their paramagnetic charge states as a function of doping, irradiation dose, and annealing temperature.
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