Study of the homogeneity of CdTe-THM monolithic nuclear detector arrays: the role of electron lifetime and leakage current

For nuclear imaging systems, CdTe-THM already has been shown to be an appropriate material. However, the homogeneity in the detector array material is still the main property that has to be improved, especially for thick detectors that are necessary for achieving a high counting rate efficiency. Apart from the standard material defects, i.e., grain boundaries, Te-precipitates, etc., electron lifetime and resistivity seem to be the major electric properties inducing or expressing the heterogeneity. Therefore, detector arrays with noticeable spread detection values have been investigated. Results are compared with energy resolution and counting rate efficiency. As expected, energy resolution is highly dependent on the electron lifetime and, to a lesser extent, on the leakage current. Their homogeneity is also discussed, but no correlation has been found between the electrical properties and the counting rate efficiency. This last parameter seems to be independent of the electrical properties, unlike the structural defects. This fact explains the large difference between pixels and why a pixel can give good ⁵⁷Co spectra with poor efficiency, and vice versa.