Temperature Dependence of Average Energy Per Pair in Semiconductor Detectors

An accurate measurement of the average energy lost by charged particles per hole-electron pair produced in semiconductor detectors as a function of temperature is desirable in view of the recently noted response of detectors at low temperatures. A simple model for the value of ϵ, the average energy per hole-electron pair, was proposed by Shockley in 1960. This model has been extended in the present work to predict temperature effects upon ϵ. Silicon and germanium lithium-drifted counters were designed and built for detecting 1 Mev electrons and/or 5.5 Mev alphas over a temperature range of 4°K to 300°K. Techniques and the necessary equipment to measure the charged produced from a single indident ionizing particle within 0.4% were developed. Data were taken for silicon and germanium detectors for temperature ranging from 20°K to 300°K. These data only qualitatively agree with the simple model. The evidence points to an additional effect over the ones invoked by Shockley. The room temperature values of ϵ for the silicon lithium-drifted counters observed in the present experiment agree with those for silicon surface barrier detectors which were recently published.