Gamma Irradiation of Silicon. III. Levels in p-Type Material

60Co gamma irradiation of p-type silicon produces donors in the lower half of the forbidden gap. From the temperature dependence of the electrical properties, a level 0.35 eV above the valence band was located for the case of silicon pulled from silica crucibles. For the case of float-zone silicon, two levels 0.21 and 0.28 eV above the valence band were found. The 0.35-eV level is introduced at the rate of 10−4 net donors/cm3 per photons/cm2. The introduction rate for the 0.21-eV level is lower than that for the 0.35 level, and that for the 0.27-eV level is so low that it was difficult to measure.