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We report here on the optimization of 0.5 cm thick pixelated Orbotech CZT detectors with regards to the
best contacting materials and the use of steering grids. We evaluated the performance of different contacting
materials. Our study differs from earlier ones in that we investigated the performance of different anode and
cathode materials separately. We obtain the best performance with Au cathodes. For different anode materials
Ti and In give the best energy resolutions. The detector (2.0×2.0×0.5 cm3, 8×8 pixels) shows excellent 59 keV,
122 keV and 662 keV energy resolutions of 1.4 keV, 1.9 keV, and 7.4 keV, respectively. Furthermore, we report
on using steering grids to improve on the performance of the pixelated detectors. Previously, the benefit of
steering grids had been limited by additional electronic noise associated with currents between the negatively
biased steering grids and the anode pixels. We are currently exploring the possibility to isolate the steering grid
from the CZT substrates by a thin layer of Al2O3. We performed a series of measurements to determine by
how much the isolation layer reduces the grid-pixel currents. Comparing the currents between two Au contacts
before and after isolating one of the two contacts from the CZT with a 700 nm thick layer of Al2O3, we measure
that the isolation layer reduces the currents by a factor of about 10 at 500 V. We present some results from
a detector before and after deposition of an isolated steering grid. The grid indeed improves on the detectors
energy resolution and detection efficiency. We show that simulations can be used to model the anode to cathode
charge correlation in excellent agreement with the experimental results.
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