Investigation of the radiation damage of GaAs detectors by protons, pions and neutrons

Surface barrier detectors processed in Aachen using SI-GaAs from several manufacturers have been irradiated with high fluences of neutrons (mean energy 1 MeV, fluence up to Φn ∼ 5 × 1014cm−2), pions (191 MeV, fluence up to Φπ ∼ 0.6 × 1014cm−2) and protons (23 GeV, fluence up to Φp ∼ 2 × 1014cm−2). The detectors have been characterized in terms of macroscopic quantities like I-V characteristic curves and charge collection efficiencies for incident minimum ionizing- (mip) as well as α-particles. All detectors work well after the exposure. At the highest fluences a sizable degradation concerning the charge collection efficiencies has been observed for all investigated materials. SI-GaAs material with low carbon content (LC material from FCM, Freiberg) seems to be less affected than substrates with a higher carbon concentration. At the highest irradiation level the mip signal from a 250 μm thick detector made of LC material amounts to 8000 electrons (at 400 V bias voltage) independent of peaking times between 40 ns and 2.2 μs. The leakage currents for this material are even reduced after the irradiation.