Optimization of quasi-hemispherical CdZnTe detectors by means of first principles simulation

In this paper we present the development of quasi-hemispherical gamma-ray detectors based on CdZnTe. Among the possible single-polarity electrode configurations, such as coplanar, pixelated, or virtual Frisch-grid geometries, quasi-hemispherical detectors are the most cost-effective alternative with comparable raw energy resolution in the high and low energy range. The optimal configuration of the sensor in terms of dimension of the crystals and electrode specifications has been first determined by simulations, and successively validated with experimental measures. Spectra from different sources have been acquired to evaluate the detectors performances. Three types of detectors with different CZT volumes have been fabricated, namely 10 × 10 × 5 mm3, 15 × 15 × 10 mm3 and 20 × 20 × 10 mm3. In the case of 10 × 10 × 5 mm3 crystals, the optimum pixel size determined by our simulation tool was confirmed by experiments: the best spectroscopic resolution of 1.3% at 662 keV has been found for a 750 μm diameter pixel detector. The best energy resolution values obtained for the 15 × 15 × 10 mm3 and 20 × 20 × 10 mm3 detectors were respectively 1.7% and 2.7% at 662 keV.