Electron Bombardment of Silicon

Abstract

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°K 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 ${\mathrm{cm}}^{-1\mathrm{}}$, 0.5 ${\mathrm{cm}}^{-1\mathrm{}}$, and 0.05 ${\mathrm{cm}}^{-1\mathrm{}}$, 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 ${\mathrm{cm}}^{-1\mathrm{}}$ and roughly 0.3 ${\mathrm{cm}}^{-1\mathrm{}}$, 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°K and 10°K show that the net damage rate decreases by a factor of 2 or more when bombardments are carried out at lower temperatures.