A SURVEY OF THE PHYSICAL PROCESSES WHICH DETERMINE THE RESPONSE FUNCTION OF SILICON DETECTORS TO ALPHA-PARTICLES

The spectra of monoenergetic alpha particles exhibit a well known asym metric shape when measured with silicon detectors. The processes are d escribed which determine the response of silicon detectors to alpha pa rticles, particularly the energy dependence of the line shape. In this work particle implanted and passivated silicon (PIPS) detectors are a ssumed to have a thin dead layer at the front contact and an infinite sensitive volume. The incoming monoenergetic alpha particles lose ener gy in the dead layer where they develop a Gaussian energy distribution due to electronic energy-loss straggling. In the sensitive volume the alpha particles transfer most of their energy to electronic excitatio n and ionization (E(s,e)) and the remaining fraction to the production of lattice vibrations and crystal damage. The statistical distributio n of E(s,e) has been calculated by Monte Carlo simulation and shown to be asymmetric. The energy E(s,e) is subsequently used for the creatio n of electron-hole pairs, which are measured by an amplifier system wi th a Gaussian contribution to the energy resolution due to electronic noise. This model permits a quantitative calculation of the detector r esponse function to alpha particles, and the result is in excellent ag reement with measured spectra. On the basis of this model the energy d ependence of the alpha particle line shape is also discussed.