Precision Measurements of the Ionization Energy and Its Temperature Variation in High Purity Silicon Radiation Detectors

Abstract

High precision absolute measurements of the ionization energy (ε) for alpha particles and electrons have been made in two thick high purity silicon guard ring detectors between 100 K and 250 K. At a fixed energy (E) both εα and εe- were found to vary linearly (r = 0.999) with the band gap (WG). εα and εe- also increased with E and εe- α εα. The slope (Δεa/ΔWG) = 1.83 ± 0.04 is the lowest so far reported and is in closer agreement with Drummond and Moll's theoretical value of 1.73. However (Δe-/ΔWG) = 2.87 ± 0.07 is significantly higher. The measured values of ε in electron volts per hole pair (eV/ehp) are: Ee- = 975.2 keV Eα = 5483 Kev εe- (300 K) = 3.631 εα (300 K) = 3.625 εe-(100 K) = 3.745 εα (100 K) = 3.698 The estimated probable error is ± 0.0025 eV/ehp. The εα values are close to other recent published results. These results taken in conjunction with earlier reported work on Si, Ge, GaAs and CdTe suggest that (Δε/ΔWG)≃ 1.8 in all these semiconductors, i.e. over the WG range from 0.7 to 1.6 eV. Therefore there is a need for further ε measurements on high purity samples of all four materials.