Characterization of photon counting pixel detectors based on semi-insulating GaAs sensor material

Hybrid semiconductor pixel detectors are considered of high interest for synchrotron applications like diffraction and imaging experiments. However, at photon energies above 30 keV, high-Z sensor materials have to be used due to the weak absorption of the most commonly used sensor material, for instance silicon wafers with a thickness of a few hundred μm. Besides materials like CdTe and Ge, semi-insulating, chromium compensated SI-GaAs(Cr) proves to be a promising sensor material for applications with X-rays in the mid-energy range up to ~60 keV. In this work, material characterisation of SI-GaAs(Cr) wafers by electrical measurements and synchrotron white beam topography as well as the characterization and application of pixel detector assemblies based on Medipix readout chips bump-bonded to 500 μm thick SI-GaAs(Cr) sensors are presented. The results show a very homogeneous material with high resistivity and good electrical properties of the electrons as well as a very promising imaging performance of the detector assemblies.