The Czech Republic and JINR. Long-Term Fruitful

All current systems use silicon as the detecting diode layer. Silicon is by far the most
perfect and most available material, but has the great drawback that the stopping power for
photons above 20 keV, an area of increasing importance at storage rings, is limited. Other
fields of X-ray imaging, notably medical imaging, face the same problem. Therefore, a lot of
investments have been made for development of other materials that work at room
temperature, like GaAs and Cd(Zn)Te.
The medical imaging industry has mainly invested in Cd(Zn)Te, since for their main
applications (humans) high energies, above 100 keV, are needed, which requires very high-Z
sensors. However, despite the large efforts invested over the years, the material quality of
Cd(Zn)Te, especially for large areas, is still far from perfect. In photon science there is a large
and growing emphasis on the energy range up to 60 to 80 keV, for which GaAs is very well
suited. A 300 micron thick, fully depleted GaAs sensor will give an order of magnitude
improvement in quantum efficiency at 40 keV. An increased absorption of the sensor
automatically gives a better shielding of the sensitive underlying CMOS readout electronics
(ASIC) as well.
The goals of this Czech (S.Pospíšil, I.Štekl, et al.) and JINR (G. Shelkov, A.
Zhemchugov, V.Elkin, V.Kruchonok, D.Kharchenko) collaboration are the development of
the necessary technology to produce GaAs-based hybrid pixel detectors and the construction
of a large area pixellated detector.
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