Simulated performance of high-Z detectors with Medipix3 readout

Abstract

The Medipix3 hybrid pixel readout chip incorporates "charge summing" circuitry, which sums together signals detected in adjacent pixels to reconstruct individual hits. This should compensate for fluorescence and charge sharing effects which degrade the performance of high-Z semiconductor detectors such as germanium, gallium arsenide and cadmium telluride. The behaviour of different high-Z sensors read out by Medipix3 is simulated, to compare their performance and to test the effectiveness of a proposed new inter-pixel communication scheme. The effects of charge sharing are eliminated in all these sensors. In Ge and GaAs sensors with 55 μm pixels, fluorescence effects only cause a small reduction in detector performance, immediately above the k-edge energy. The improvement in spectral performance makes it easier to deal with charge trapping effects in GaAs; with an electron lifetime of 10 ns, the main result of charge trapping is a tolerable reduction in energy resolution. In CdTe, fluorescence effects strongly degrade the spatial resolution above the k-edge energy of 26.7 keV, but with appropriate threshold settings the resolution can be recovered at energies above 35 keV. When CdTe is used in colour mode with 110 μm pixels, charge summing greatly reduces the escape and fluorescence peaks in the spectral response. Finally, since the charge summing circuitry cannot correct parallax effects, parallax will become the main source of blurring in the detector in many X-ray scattering experiments.