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

The radiation damage in 100 μm thick Schottky diodes made on semi-insulating undoped GaAs materials, were studied using α-, β-, proton- and γ-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 α-spectra in overdepleted detectors, the charge collection efficiency for β-particles, cceβ, is well predicted in the unirradiated detectors, while in the most irradiated ones, the cceβ 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.