Microstrip X-ray detector with a very high dynamic range based on LPE-GaAs

We report on the fabrication and characterization of a microstrip X-ray detector with a very high dynamic range based on GaAs diodes. The detector material was grown by liquid phase epitaxy (LPE) and showed a typical n-type background doping of 2×10¹³ cm^-3 . The thickness of the epitaxial layer was between 75 and 200 μm. At 27 V bias the thickness of the active layer was 45 μm. The detector consists of 48 strips with a pitch of 50 μm and a strip length of 3 mm. No cross talk between the diodes was observed, Measurements using a micro focus X-ray tube showed a mean quantum efficiency of the detector for the energy range between 35 and 100 keV of 9.5%. The maximum contrast was a factor of 400 between the signal in areas that were not shaded with lead and areas that were shaded with 5 mm lead. The maximum counting rate without amplifier saturation was 4.5×10⁵ per second, which gives a dynamic range of 4.5×10⁵ above 25 keV. The high dynamic range of this kind of X-ray detectors makes them very interesting for non destructive material testing