Shallow donor centers produced in silicon after erbium implantation and subsequent annealing at 700 deg C have been studied. Besides the formation of oxygen-related donors with ionization energies between 0.03 eV and 0.04 eV, other donor states at approxE_c-0.07 eV are introduced and they are attributed to erbium-related centers. Additional heat treatment of Er-implanted oxygen-rich layers at 450 C leads to the appearance of Thermal Double Donors as well as a considerable increase in the concentration of oxygen-related donors at approxE_c -0.04 eV. The erbium-related donors were found to be insesnitive to the oxygen aggregation taking place at 450 deg C.
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