Semi-insulating Fe-doped wafers were irradiated with 2.2MeV electrons at 4.5K, to doses of between 2 x 1017 and 3 x 1018/cm2. They were then studied by making magnetic circular dichroism measurements of the optical absorption, and of the infra-red absorption behavior. Two new magnetic circular dichroism spectra were observed after irradiation. They increased linearly with dose, and were attributed to close Frenkel pairs. These spectra annealed out at about 200K (stage-I) and appeared to provide spectroscopic evidence for intrinsic defects that annealed out below room temperature. Together with annealing of these close Frenkel pairs, 2 well-known magnetic circular dichroism spectra appeared which had been attributed to the PIn antisite and to impurity-defect complexes. The impurity-defect complexes annealed out at temperatures of between 330 and 400K (stage-II) whereas final annealing out of the PIn antisites was observed at about 650K. Coincidentally with this final annealing, the magnetic circular dichroism band of the Fe acceptor completely recovered. A familiar infra-red absorption band (with a phonon energy of more than 0.77eV) was shown to form directly during irradiation.

H.Hausmann, P.Ehrhart: Physical Review B, 1995, 51[24], 17542-50