Impact production of secondary electronic excitations in insulators: Multiple-parabolic-branch band model

Analytic expressions for threshold energies and rates of electron-hole pair and exciton productions by electron impact in wide-gap insulators are given within a multiple-parabolic-branch band model which goes beyond the single-parabolic-branch model. The analysis is based on the polarization approximation. Due to the transition between the different branches, the thresholds are significantly lower than those for the single-parabolic-branch band model, and the exponents of power laws of the partial production rates are higher by 1. The interaction between components of the electron-hole pairs reduces exponents by 0.5 for both band models; an exciton reduces them by 1.5. The account for inelastic scattering with phonon emission can explain the shift of an experimentally observed threshold to higher energies. The calculated threshold of exciton production for solid Xe is in good agreement with the experimental one.