MICRO STRIP X-RAY-DETECTOR WITH A VERY HIGH DYNAMIC-RANGE BASED ON LPE-GAAS

We report on the fabrication and characterization of a microstrip x-ra y detector with a very high dynamic range based on GaAs diodes. The de tector material was grown by Liquid Phase Epitaxie (LPE) and showed a typical n-type background doping of 2 x 10(13)cm(-3). The thickness of the epitaxial layer was between 75 and 200 mu m. At 27 V bias the thi ckness of the active layer was 45 mu m. The detector consists of 48 st rips with a pitch of 50 mu m and a strip length of 3 mm. No cross talk between the diodes was observed. Measurements using a micro focus x-r ay tube showed a mean quantum efficiency of the detector for the energ y range between 35 and 100 keV of 9.5%. The maximum contrast was a fac tor 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 w ithout amplifier saturation was 4.5 x 10(5) per second, which gives a dynamic range of 4.5 x 10(5) above 25 keV, The high dynamic range of t his kind of x-ray detectors makes them very interesting for non destru ctive material testing.