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

The radiation damage in 100 mu m thick Schottky diodes made on semi-insulat ing undoped GaAs materials, were studied using alpha-, beta-, proton- and g amma-spectroscopy as well as I-V measurements. The results have been analys ed within the framework of the Hecht model to investigate the influence of the plasma produced by short-range strongly ionising particles on the detec tor performance after 24 GeV proton irradiation. It has been found that wit h the mean free drift lengths for electrons and holes determined from alpha -spectra in overdepleted detectors, the charge collection efficiency for be ta-particles, cce(beta), is well predicted in the unirradiated detectors, w hile in the most irradiated ones, the cce(beta) is underestimated by more t han 40%. The observed disagreement can be explained by assuming that the ch arge carrier recombination in the plasma region of such detectors, becomes significant. (C) 1999 Elsevier Science B.V. All rights reserved.