Electron Bombardment of Silicon

The electrical properties of single crystal silicon have been investigated as a function of bombardment with high-energy electrons. Measurements of the initial carrier removal rate were carried out at 273^ for samples with widely different carrier concentrations. A second type of experiment involved the measurement of the temperature dependence of resistivity and Hall coefficient at different stages of the bombardment. Bombardment-produced energy levels were found at 0. 03 ev, 0. 17 ev, and 0. 4 ev below the edge of the conduction band. With 4. 5-Mev electrons, the introduction rates for these levels were 11 cm^-1, 0. 5 cm^-1, and 0. 05 cm^-1, respectively, Bombardment levels were also found at 0. 05 ev and 0. 3 ev above the edge of the valence band. With 4. 5-Mev electrons the introduction rates for these levels were 13 cm^-1 and roughly 0. 3 cm^-1, respectively. Irradiations with 700-kev electrons indicate the presence of the same defect levels with correspondingly smaller introduction rates. An investigation of the irradiation-induced mobility changes for degenerate p-type silicon indicates that, for each hole removed from the valence band, there appears a singly-charged scattering center. For near-degenerate n-type samples, the mobility changes are much smaller. Results of bombardments at 78^ and 10^ show that the net damage rate decreases by a factor of 2 or more when bombardments are carried out at lower temperatures.