Radiation ionization energy in alpha-Si:H

The radiation ionization energy epsilon(p), which is the mean energy expended per electron-hole pair generated in a given material by an ionizing radiation, is one of the most important parameters governing the properties of radiation detectors based on this material. Since the advent of semiconductor detectors in the 1950s, a great deal of experimental and theoretical work has been done to determine values of epsilon(p) for various crystalline semiconductors. After some review of the theoretical models proposed for crystalline semiconductors, we present a detailed study for an amorphous semiconductor. A microscopic Monte Carlo calculation, taking into account the actual density of states, was performed in a-Si:H to study the energy sharing between ionization and phonon production during hot carrier thermalization. This simulation yields values from 4.3 to 5.0 eV for epsilon p for reasonable values of the phonon emission mean free path lambda(r) in a-Si:H. This result is in agreement with experimental results of about 4.4 eV and are comparable to 3.63 eV in crystalline silicon, despite the larger 1.7-eV gap.