| Cadmium zinc telluride (CdZnTe) is a wide bandgap semiconductor material thathas been studied extensively for x-ray and gamma ray detectors. Recent improvementsin growth techniques have improved the CdZnTe material quality and charge transportproperties, resulting in detectors with improved energy resolution. This has opened awide field of potential applications of CdZnTe detectors for national security, medical,space, basic science and environmental mitigation and safety.Compared with gas detectors and scintillator detectors, the semiconductor detectorcan provides better image, energy resolution, and a more compact system structure.Especially for the most resent three years, the implement of national space stationprogram and the establishment of the national science facilities, which include theprototype of “ShenGuang III” and the Large Sky Area Multi-Object FiberSpectroscopy Telescope (LAMOST), provide new platforms for development ofhigh energy physics and astronomy technology of our nation. Therefore, thecorresponding scientific research subjects have emerged that are simulated bythese great national science facilities. And there are many new requirements fordiagnostic and detect technique of high energy.Because of the high atomic number, the high density and the wide band gap,CdZnTe detectors have a capable of high detection efficiency, good room temperatureperformance and are very attractive for X-ray and gamma ray applications, especiallyfor the measurements between100keV and1MeV. In some application, its detectionefficiency will be more than90%.The prominent properties of CdZnTe detectors benefit more and more from thedevelopment of crystal growth methods and techniques, optimizing of detector structure,and improvement of signal processing techniques. So, the CdZnTe detector has becomea hot point in the research of semiconductor room-temperature radiation detectors, andit has attracted increasing interest by many researchers from developed nations.As for now, the domestic research is still in its infancy which focuses on the crystalgrowth and its surface process. By contrast, the overseas researchers dedicate to thenovel structure electrode, the improvement of plus signal processing and the physicalmechanism of carrier tapping. Despite all its advances in many technology, there areseveral realistic problems. In order to fix the structural system of CdZnTe detector and to expand scope of itsapplication, we have conducted research on the pixellated CdZnTe detector. Thisresearch are supported by National Natural Science Foundation of China (No.10876044,No.62174048) and the fundamental research funds for the central universities(CDJXS11122219). The main work of this thesis are provided as follows:(1) The principles of interaction mechanisms between radiation particles andmaterials are introduced. The relationship between these mechanisms and photon energyis discussed. Based on weighting potential theory, it analyses the principle of generatingsignals and charge collection. And the theory of unipolar detectors is discussed. Thispart also sums up the readout system of detectors.(2) The main physical process within the detector martial have been simulated bythe MCNP code, which includes photoelectric effect, Compton scattering,electron-positron pair and rayleigh scattering. And then, the inner electric field ismodeled by Matlab. It has analyzed the relationship between the electrode structure anddistribution of weighting potentials. At last, the spectra from different sources areprovided, and the corresponding analysis is based on Shockley-Ramo theory.(3) Some pixellated CdZnTe are fabricated in our laboratory. The surface leakagecurrents of these pixel array electrodes are tested and analyzed based on the leakagetheory of pixellated CdZnTe detector. The leakage current map are provided. And thefollowing research includs:(a)The energy resolution in different operation condition.(b)The charge sharing and loss within gaps are discussed.(c)The detector dimension is optimized based on energy deposition, chargecollection efficiency and energy resolution.(d)The spectrum and image of137Cs are obtained through a thick pinhole system.(4)The further process of polarization within a pixellated CdZnTe detector underintense X-ray irradiation is studied by dual-radiation method. According to the extendpolarization level, the flux of X-ray is estimated. At last, the critical density ofpolarization is deduced. And the relationship between polarized region and space chargediffusion is discussed. It is a a supplement of the dynamic polarization theory, and itprovides an evidence of diffusion within the CdZnTe under intense irradiation. |
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