Electrical properties of electron-irradiated n-type silicon

Investigations of electron-irradiated n-type silicon show that the conductivity decreases with increasing dose, achieves intrinsic value, then converts into p type and increases again, reaching a saturation value. It is shown analytically that this behavior [for float-zone silicon irradiated in the (111) direction] can be described by assuming that three main damage levels (two acceptor levels and one donor level) occur simultanously due to the irradiation. The deepest acceptor level determines the dose at which the minimum value of the conductivity occurs. The two acceptor levels (at E/sub c/-0.44 eV and E/sub c/-0.58 eV) are responsible for the decrease in conductivity at low doses. When the density of damage centers at E/sub c/-0.58 eV exceeds the initial doping concentration, emission of holes from this level gives a significant contribution to the conductivity causing the conductivity to increase with dose. The donor level at E/sub v/+0.27 eV causes the saturation at large doses. A zero-current approximation is given for the conductivity versus dose dependence for an unlimited number of levels involved. These levels may be either independent levels or levels associated with different charge states of the same defect. By introducing the three levels above in this model a very good agreement with experiments on dose versus conductivity was obtained in the resistivity range 100 Ω cm to 50 KΩ cm. The results indicate that the two acceptor levels at E/sub c/-0.44 eV and E/sub c/-0.58 eV may be associated with the single- and double-charge state, respectively, of the divacancy