High-spatial resolution measurements with a GaAs:Cr sensor using the charge integrating MONCH detector with a pixel pitch of 25μm

The aim of this project is to determine the imaging capabilities of a 25 mu m pixel pitch GaAs:Cr sensor of 500 mu m thickness bump-bonded to the charge integrating MONCH 03 readout chip (also called GaAs-MONCH assembly) and to assess the possibility to improve the spatial resolution by applying a position interpolation algorithm developed at PSI. Measurements were performed at the TOMCAT beamline of the Swiss Light Source (SLS) using photon beams in the energy range of 10-30 keV. The imaging experiments indicate the possibility to enhance the spatial resolution of the detector beyond its actual physical pixel pitch. We have quantified the spatial resolution of a GaAs-MONCH assembly by means of the modulation transfer function (MTF), achieving 10 mu m at 10 keV and 12 mu m at 20 keV photon energies. By applying a modified interpolation algorithm, a spatial resolution of similar to 5 mu m was obtained for 16 keV when binning to 2.5 mu m virtual pixels, while with the silicon-MONCH assembly, we achieved a spatial resolution of 3.5 mu m, which serves as gold standard. The results are promising because they open new possibilities to perform imaging measurements using the GaAs-MONCH assembly at photon energies above 15 keV, where silicon sensors suffer from a diminishing quantum efficiency.