N-type silicon conductivity conversion under the action of high-speed helium ions

As a result of irradiation by fast helium ions and annealing of radiation damages in the temperature interval from 350 to 5000C, electronic silicon changes its conductivity type. Observations are performed on specimens of ''crucible'' n-type silicon doped with phosphorus, the initial resistivity being 30 and 130 ohm.cm. Irradiation was carried out by 25 MeV helium ions with an integral flux of 1.1012ions cm-2. The properties of the irradiated specimens are investigated with the help of single-probe technique by thermo-probe method and current-voltage characteristics. In low-resistance specimen the n-p conversion is observed in a layer of radiation-damaged silicon bulk near the limit of particle penetration. In high-resistance specimens the conversion layer width has grown almost to dimensions of the irradiated volume. The observed conductivity conversion in n-silicon seems to be connected with the formation of vacancy clusters