ABSTRACT
Efforts have long been made to develop room temperature semiconductors with high atomic numbers and wide band gaps. These materials are useful not only in medical and industrial imaging systems, but also in detectors for high-energy particle astrophysics and astrophysics in general. Among the range of semiconductor detectors available for gamma-ray detection, CdTe and CdZnTe occupy a privileged position due to their high density, the high atomic number of their components, and a wide band gap. A large band gap energy (Egap = 1.44 eV) allows us to operate these detectors at room temperature.1-4
The high absorption efciency of cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe)—comparable with that of NaI and CsI-is a very attractive feature.
8.1 Introduction .................................................................................................. 171 8.2 High-Resolution CdTe Detector ................................................................... 173 8.3 CdTe Pixel Detector Module ........................................................................ 176 8.4 Stacked CdTe Detector ................................................................................. 178 8.5 CdTe Double-Sided Strip Detector ............................................................... 181 8.6 Si/CdTe and CdTe/CdTe Semiconductor Compton Camera ......................... 184 8.7 Conclusion .................................................................................................... 187 Acknowledgments .................................................................................................. 188 References .............................................................................................................. 189
As shown in Figure 8.1, photoelectric absorption is the main process up to 300 keV for these materials, as compared to 60 keV for silicon. Therefore, CdTe and CdZnTe are expected to become more efcient once the gamma-ray energy exceeds a few hundred kilo-electron volts. Despite long-term efforts to make improvements, however, high-resolution CdTe and CdZnTe detectors with energy resolution better than a few kilo-electron volts (full width at half maximum or FWHM) have only recently become available. In the 1990s, remarkable progress in the technology for producing high-quality single crystals of CdTe by using the traveling heater method (THM)5 and CdZnTe by using the high-pressure Bridgman (HPB) technique6-8 dramatically changed high-resolution room temperature detectors. The industry has further continued such efforts in the 2000s toward producing high-quality CdTe and CdZnTe wafers.9-13 In addition to progress regarding the crystal, various technologies of electrode conguration have been proposed and developed to overcome poor carrier transport in the device, as described in this chapter.
