Performance improvement of large volume CdZnTe detectors

The paper analyzes results of several projects devoted to manufacturing of large volume CZT detectors for safeguard purposes. It is shown that the final performance of such detectors depends on the quality of crystals, design of detectors and technology of their manufacturing. Coplanar grid contacts applied for the detectors based on 15×15×10 mm³ crystals grown by different producers have also proved to perform well. The paper also analyzes the results of the inspection test of crystals which evidence that there is progress in growing high-quality crystals. The detectors were made by basic technology developed at the BSI for pixel and strip detectors, using special technological processes to obtain high intergrid resistivity and spectrometric performance. Despite the branched structure of coplanar grid contacts, the intergrid resistance of about 5-6 GOhm was achieved. Analysis of the differences in I-V and spectrometric characteristics of the detectors based on crystals grown by different manufacturers shows that there is high reproducibility of results for Yinnel Tech company´s crystals. All detectors with a crystal volume of 15×15×10 mm³ with varying contact topology have the total absorption efficiency of registration about 8%, energy resolution less than 2% on the energy 662 keV and the peak/Compton ratio better than 11. The best energy resolution of 10.5 keV (1.59%) was achieved at HV=2 kV and the optimal voltage of 60 V between the grids. The energy resolution of the detectors on energies 59.6 and 1332 keV was 7.9 and 14.5 keV, respectively.