High efficiency pixellated CdTe detector

Position sensitive detectors constructed from compound semiconductors (CdTe, CdZnTe, HgI2) are being developed for a variety of applications where high sensitivity and improved energy resolution are significant advantages over scintillator or gas based systems. We have investigated the possibility of using a CdTe detector array in a SPECT gamma camera that would require a high efficiency at 140 keV. The problem of worsening photopeak efficiencies in thick detectors (due to incomplete charge collection) makes it difficult to maintain a high efficiency which, ironically, is the primary reason for choosing a thicker detector. Recent research has shown that following a simple geometrical design criterion can greatly reduce this deleterious effect. This paper reports on the results from a small prototype pixellated array fabricated using this design. We verify the ‘small pixel effect’ for a detector thickness and pixel size significantly larger than those used in most other work. A 9-element detector (1×1 mm pixels, 4 mm thick) has been fabricated and characterized in terms of energy resolution, peak-to-valley ratio and detection efficiency. Testing of the detector in a fast pulse mode to obtain its high count rate response has also been performed.