Applications of Monte Carlo Methods to Simulate Gamma Ray Interactions in Si and Ge

A Monte Carlo code is employed to simulate the electron cascade subsequent to a gamma ray interaction in two common semiconductors, silicon and germanium, over the energy range of 50 eV to 2 MeV. The partitioning of the gamma ray energy into the various loss mechanisms determines the performance of the detector, generally parameterized by the average energy to create a charge carrier pair, W, and the intrinsic variance or Fano factor, F. In this work, W and F are found as a function of energy, exhibiting saw-toothed variation at the shell edges and a well defined high energy value well above the K edge. Our calculated results are in agreement with experiment Valence to conduction interband transitions and plasmon excitations are the dominant source of electron-hole pairs.