Investigating the suitability of GaAs:Cr material for high flux X-ray imaging

Semi-insulating wafers of GaAs material with a thickness of 500 mu m have been compensated with chromium by Tomsk State University. Initial measurements have shown the material to have high resistivity (3 x 10(9) Omega cm) and tests with pixel detectors on a 250 mu m pitch produced uniform spectroscopic performance across an 80 x 80 pixel array. At present, there is a lack of detectors that are capable of operating at high X-ray fluxes (> 10(8) photons s(-1) mm(-2)) in the energy range 5-50 keV. Under these conditions, the poor stopping power of silicon, as well as issues with radiation hardness, severely degrade the performance of traditional detectors. While high-Z materials such as CdTe and CdZnTe may have much greater stopping power, the formation of space charge within these detectors degrades detector performance. Initial measurements made with GaAs:Cr detectors suggest that many of its material properties make it suitable for these challenging conditions. In this paper the radiation hardness of the GaAs: Cr material has been measured on the B16 beam line at the Diamond Light Source synchrotron. Small pixel detectors were bonded to the STFC Hexitec ASIC and were irradiated with 3 x 10(8) photons s(-1) mm(-2) monochromatic 12 keV X-rays up to a maximum dose of 0.6 MGy. Measurements of the spectroscopic performance before and after irradiation have been used to assess the extent of the radiation damage.