Modelling and 3D optimisation of CdTe pixels detector array geometry - Extension to small pixels

CdTe and CdZnTe pixel detectors offer great interest for many applications, especially for medical and industrial imaging. Up to now, the material, ge nerally, used and investigated for pixel arrays was CZT (Hamel et at., IEEE Trans. Nucl. Sci. 43 (3) (1996) 1422; Barrett et al., Phys. Rev. Lett. 75 (1) (1995) 156; Bennett et al., Nucl. Instr. and Meth. A 392 (1997) 260; Es kin et al., J. Appl. Phys. 85 (2) (1999) 647; Brunett et al., J. Appl. Phys . 86 (7) (1999) 3926; Luke, Nucl. Instr. and Meth. A 380 (1996) 232), but c admium telluride can also be an appropriate choice, as shown here. However, we clearly demonstrate here that the optimal pixel configuration is highly dependent on the electrical transport properties of the material. Dependin g on the field of primary interest, either energy resolution or counting ra te efficiency in the photopeak, the geometry for each case has to be optimi sed. For that purpose, we have developed a calculation of the signal induce d onto the pixel. Two distinct parts are used: after showing our approach f or the weighting potential calculation, we present our results performed by a "pseudo-Monte Carlo" simulation. Results are supported by a few experime ntal comparisons. We argue about. the optimum sizes with clarifying the pro blems caused by too small and too large pixel sizes. The study field is cho sen to be vast, i.e. pixel size to detector thickness ratios (W/L) of 1/8-1 , and detector thickness of 1.0-8.0 mm. In addition, several electrical tra nsport properties are used. Since efficiency is often of primary interest, thick detectors could be very attractive, which are shown to be really feas ible even on CdTe. (C) 2001 Elsevier Science B.V. All rights reserved.