COMPARISON OF SIGNAL RISE-TIMES IN TOTALLY DEPLETED P-TYPE AND N-TYPESILICON SURFACE-BARRIER DETECTORS

The rise-times of charge collection signals from the incidence of prot ons and alpha-particles of energies up to 25 MeV have been measured fo r totally depleted silicon surface barrier type detectors made from P- type and N-type silicon. The detectors were of similar thickness and t he resistivities of the bulk materials such that their depletion volta ges were comparable. The measurements show that P-type detectors can g ive at least as good particle identification by signal rise-time as ca n N-type detectors. Analyses of the experimental data show that the pr evious simple theory of charge collection rise-time identification has to be modified to take account of the finite internal space charge fi elds in the plasma columns along the particle tracks. The theory must also include contributions from the movement of holes. The velocities of electrons and holes deduced via this theory from the experimental d ata show a ratio which does not agree for mobility dominated velocitie s.