X-ray detectors made of self-supported epitaxial GaAs

We first show that GaAs is adapted to X-ray imaging because it corresponds to a value of the atomic number which realizes the best balance between contrast, spatial resolution and absorption efficiency. Moreover, the material adapted to imaging should have a low and uniform defect concentration, which implies the use of thick epitaxial GaAs layers. Finally, because pixel detectors, processed on one surface, are bump bonded on an ASIC, the X-ray irradiation must be applied on the opposite surface. This additional condition implies that imagers should be made of self-supported epitaxial layers to prevent the attenuation of the X-ray flux in the substrate. We describe the way to obtain such type of layers and the characteristics of detectors made with them.