【作者】 王玺；

【导师】 肖沙里；

【作者基本信息】 重庆大学 ， 光学工程， 2013， 博士

【摘要】 近年来，半导体核辐射探测器的发展相当迅速。这类探测器已经广泛地应用于核物理学、X射线和伽玛射线天文学，以及核医学等诸多领域。与气体探测器和闪烁体探测器相比，半导体探测器的成像性能更为优异，能谱分辨能力也更强，同时还可以使整个探测系统的结构更为紧凑。特别是最近三年来，“神光-III原型”及“LAMOST”等国家大型科学装置的落成，为我国核物理学、高能物理学和天体物理学等诸多研究提供了新平台，开拓了新领域，提供了新契机，为取得进一步重大科研成果奠定了坚实的基础。因此，已经形成了以大科学装置为基础的一系列后续科研课题，产生了对高能射线能谱探测及成像诊断技术的新需求。CdZnTe晶体材料对硬X射线和伽玛射线的截止能力和探测量子效率都很高，适合探测范围10keV~1.5MeV能量的光子，特别是在10~100keV能量范围内，其能量探测效率可以达到90%以上。不断成熟的晶体生长方法与工艺，不断优化的探测器结构以及不断完善的信号处理技术，都使得CdZnTe探测器的性能越来越优异，在核辐射探测领域起着越来越重要的作用，成为现在室温半导体辐射探测领域的热点，受到世界各国的高度重视。目前，国内外CdZnTe像素核辐射探测器的研究存在很大差距。国内相关研究工作还处于起步阶段，研究单位也相对较少，主要的研究集中在CdZnTe晶体生长工艺和表面处理技术方面；国外相关研究主要针对新型探测器电极结构的设计、探测器脉冲信号电子学处理技术的改进、以及载流子俘获的物理机制等。虽然在提高CdZnTe探测器能量分辨率的研究方面取得了很大进展，但是CdZnTe像素核辐射探测技术的相关研究领域内，还存在若干问题亟待解决。为了完善像素CdZnTe像素核辐射探测器在核辐射能谱探测及成像探测领域的结构体系，拓展其在粒子探测领域的应用范围，面向“神光III”等国家大科学装置对X射线及Gamma射线诊断的需求，以及核医学、天文物理等研究领域的需求，开展了“像素CdZnTe探测器研究”这一课题的研究工作。研究得到了国家自然科学基金面上项目(No.10876044, No.62174048)中央高校基本科研业务费资助项目(No.CDJXS11122219)的资助。围绕所提出的科学问题，按照改进CdZnTe探测器能量分辨率及成像探测性能的主旨，主要研究工作如下：(1)讨论入射光子与CdZnTe晶体相互作用的物理机制，分析了几种不同作用机制与光子能量的关系。基于权重势理论，分析了信号产生与收集原理，对单极性探测器的工作原理进行了讨论。对像素探测器的读出系统进行了总体归纳与设计。(2)模拟了X射线或伽玛射线在探测过程中的主要物理过程，以将模拟结果用于探测器的优化设计。首先采用MCNP代码建模，包括光子与晶体的主要作用机制，比如光电吸收，康普顿散射，电子偶产生以及瑞利散射等。其次利用Matlab电场有限元分析软件工具包对电荷在晶体中的俘获与扩散建立了模型。分析讨论了不同尺寸的电极结构对权重势分布的影响。最后基于Shockley-Ramo理论建立了像素探测器信号感生模型，并给出了不同辐照源的能谱结果。(3)根据对电极材料与表面处理工艺的研究，制备了不同规格像素探测器。并首先对这些探测进行了漏电测试，得到了不同偏压下像素探测器的漏电流分布，随后根据不同的探测器结构设计进行了进一步研究，内容包括：(a)研究了不同条件下，探测器的能谱分辨率。(b)对像素探测器中间隙处的电荷共享与损失进行了研究。(c)根据能量的沉积，电荷的收集效率，电荷共享，以及能量分辨率等因素对像素探测器的像素尺寸进行了综合优化。(d)通过厚针孔系统，对137Cs高能662keV伽马射线辐射源进行成像探测，得到了能谱图和放射源图像。(4)采用了双向辐照的方法，研究了深度极化的过程，并结合模拟的电势分布讨论了极化增强的原因。利用极化扩展的程度，对高通量的X射线进行了估算。最后，推导了发生极化时空间电荷的临界浓度，并与光子通量建立了数学联系，讨论了高辐照下空间电荷扩散与极化区域的关系。对极化效应进行了补充，也从另一个方面证实了空间电荷的扩散。更多还原

【Abstract】 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.更多还原