Evidence for plasma effect on charge collection efficiency in proton irradiated GaAs detectors

The radiation damage in 100 m m thick Schottky diodes made on semi-insulating undoped GaAs materials, were studied using a -, b -, proton and g spectroscopy as well as I-V measurements. The results have been analysed within the framework of the hecht model to investigate the influence of the plasma produced by short-range strongly ionising particles on the detector performance after 24 GeV proton irradiation. It has been found that with the mean free drift lengths for electrons and holes determined from a spectra in overdepleted detectors, the charge collection efficiency for beta particles cceb is well predicted in the unirradiated detectors, while in the most irradiated ones, the cceb is underestimated by more than 40%. The observed disagreement can be explained by assuming that the charge carrier recombination in the plasma region of such detectors, becomes significant.