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

Abstract

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.