The detector material Cadmium Zinc Telluride ( CZT ) achieves excellent spatial resolution and good energy resolution over a broad energy range , several keV up to some MeV .
Presently , there are two main methods to grow CZT crystals , the Modified High-Pressure Bridgman ( MHB ) and the High-Pressure Bridgman ( HPB ) process .
The study presented in this paper is based on MHB CZT substrates from the company Orbotech Medical Solutions Ltd . [ 1 ] .
Former studies have shown that high-work-function materials on the cathode side reduce the leakage current and therefore improve the energy resolution at lower energies .
None of the studies have emphasized on the anode contact material .
Therefore , we present in this paper the result of a detailed study in which for the first time the cathode material was kept constant and the anode material was varied .
We used four different anode materials : Indium , Titanium , Chromium and Gold , metals with work-functions between 4.1 eV and 5.1 eV .
The detector size was 2.0 \times 2.0 \times 0.5 cm ^ { 3 } with 8 \times 8 pixels and a pitch of 2.46 mm .
The best performance was achieved with the low work-function materials Indium and Titanium with energy resolutions of 2.0 keV ( at 59 keV ) and 1.9 keV ( at 122 keV ) for Titanium and 2.1 keV ( at 59 keV ) and 2.9 keV ( at 122 keV ) for Indium .
Taking into account the large pixel pitch of 2.46 mm , these resolutions are very competitive in comparison to those achieved with detectors made of material produced with the more expensive conventional HPB method .
We present a detailed comparison of our detector response with 3-D simulations .
The latter comparisons allow us to determine the mobility-lifetime-products ( \mu \tau -products ) for electrons and holes .
Finally , we evaluated the temperature dependency of the detector performance and \mu \tau -products .
For many applications temperature dependence is important , therefore , we extended the scope of our study to temperatures as low as -30 ^ { \circ } C. There are two important results .
The breakdown voltage increases with decreasing temperature , and electron mobility-life-time-product decreases by about 30 % over a range from 20 ^ { \circ } C to -30 ^ { \circ } C. The latter effect causes the energy resolution to deteriorate , but the concomitantly increasing breakdown voltage makes it possible to increase the applied bias voltage and restore the full performance .