Gamma Irradiation of Silicon. II. Levels in n-Type Float-Zone Material

Measurements of the electrical properties of gamma-irradiated float-zone silicon have been used to locate a number of net acceptor levels in the upper half of the forbidden gap. In material doped with less than 1016 donors, a level due to a vacancy-oxygen atom pair located 0.17 eV below the conduction band is introduced at a rate comparable to its introduction in oxygen-containing material. However, in addition there is introduced a level located 0.47 eV below the conduction band in phosphorus-doped and 0.43 eV below the conduction band in antimony-doped float-zone silicon. This latter level is presumably due to vacancy-donor complexes. Annealing above 150°C removes the deep level; further irradiation and annealing causes the reappearance of a deep net acceptor level at 0.47 eV. In irradiated and annealed silicon and additional net acceptor level at 0.21 eV below the conduction band was observed.