Detector response and performance of a 500 μm thick GaAs attached to Timepix3 in relativistic particle beams

The performance and response of a Timepix3 detector with a 500 μm thick GaAs:Cr sensor layer was investigated in different radiation fields. The sensor resistivity was ρ 109 Ω cm. Fitting different modified Hecht functions, which take the small pixel effect into account, the mobility-lifetime products of μeτe = (0.773 ± 0.018) × 10-4 cm2V-1 and μeτe = (0.996 ± 0.056) × 10-4 cm2V-1 were determined. Hereby, the latter value is favored due to the better agreement of fit and data. In a measurement in a 40 GeV/c pion beam, the drift times and charge collection efficiencies were studied as a function of the interaction depth. We present the measured drift velocity as a function of the electric field strength and compare the determined dependence with a model. In a measurement in a mixed ion beam, we study the capability of the detector to separate different ion species. We show the detector response in the form of tracks and discuss heavy ion track features.