RADIATION IONIZATION-ENERGY IN ALPHA-SIH

The radiation ionization energy epsilon(p), which is the mean energy e xpended per electron-hole pair generated in a given material by an ion izing radiation, is one of the most important parameters governing the properties of radiation detectors based on this material. Since the a dvent of semiconductor detectors in the 1950s, a great deal of experim ental and theoretical work has been done to determine values of epsilo n(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, w as performed in a-Si:H to study the energy sharing between ionization and phonon production during hot carrier thermalization. This simulati on yields values from 4.3 to 5.0 eV for epsilon p for reasonable value s of the phonon emission mean free path lambda(r) in a-Si:H. This resu lt is in agreement with experimental results of about 4.4 eV and are c omparable to 3.63 eV in crystalline silicon, despite the larger 1.7-eV gap.