Average Energy Expended Per Ionized Electron-Hole Pair in Silicon and Germanium as a Function of Temperature

Measurements have been made over a range of temperature of the amount of ionization produced by the passage of ionizing radiation through the junctions of germanium and silicon lithium-drifted solid-state detectors. These data are presented in the form of the average energy per hole-electron pair. A simple model for the value of $\epsilon$, the average energy per hole-electron pair, was proposed by Shockley in 1960. This model has been extended to predict temperature effects upon $\epsilon$. Silicon and germanium lithium-drifted counters were designed for detecting 1-MeV electrons and/or 5.5-MeV alphas over a temperature range of 4 to 300°K. The techniques and necessary equipment were designed to enable the measurement of the charge detected from a single incident ionizing particle with a probable error less than 0.4%. Data were taken on silicon and germanium detectors for temperatures ranging from 20 to 200°K. The data only qualitatively agree with the simple model. The evidence points to additional effects besides those considered by Shockley. The room temperature values of $\epsilon$ for the silicon lithium-drifted counters agree with those for silicon surface barriers which were recently published.