大尺寸TlBr单晶生长及其室温核辐射探测器的制备技术研究

TlBr is a novel wide band-gap compound semiconductor for room-temperature nuclear detectors. Compared to other compound semiconductors such as GaAs、PbI2 and CdZnTe, TlBr received more attention as a material for high energy radiation detection due to its excellent intrinsic properties and its easy growth from melt. Based on the design、simulation and fabrication of a multizone temperatue furnace with a precisely controlled temperature gradient by a plurality of heating elements, vertical gradient freezing method will be conducted to grow large volume TlBr crystals in this project. The influence of some key parameters, such as temperature gradient, growth rate, and ampoule diameter on the shape of solid-liquid boundary, crystal perfection, and electrical and optical characteristics of the obtained crystals will be systematically studied. In addition, various ambient will be conducted to control defects in the crystals. To understand the mechanism of the crystal growth and to obtain good-performance TlBr crystals with less defects, good perfection, and good electrical and optical characteristics, the dynamics of crystal growth and thermodynamics of defects will be investigated through various characterization. Furthermore, in order to produce high-performance TlBr detectors, several processing-related factors will be considered in detail, such as the method and quality of cutting, polishing and etching, the type and the configuration of electrodes, the size of the wafers and the configuration of detectors. The aim of this research is to obtain planer and pixelled room-temperature detectors with good time stability, good energy resolution and high detection efficiency.

溴化铊（TlBr）是一种非制冷型核辐射探测器用新型宽禁带化合物半导体材料，与GaAs、PbI2、CdZnTe等半导体探测材料相比，TlBr由于其物理特性优良且易于熔融生长等特点成为制备高能射线探测器的热点材料。本项目拟在设计、仿真并制作多温区精密控温晶体生长炉的基础上，利用垂直梯度凝固法生长大尺寸TlBr单晶，系统研究温度梯度、生长速率、安瓿直径等关键生长参数对大尺寸晶体的生长界面、晶体完整性及光学和电学性能的影响，以及研究晶体的气氛生长对晶体热缺陷的控制作用，结合各种表征手段来研究大尺寸TlBr晶体生长动力学机制及缺陷热力学，从而制备出结晶缺陷少、完整性好、光电特性优良的大尺寸TlBr单晶；在此基础上对探测器晶片的加工及表面处理工艺、电极材料类型及结构形式、晶片厚度、器件结构等进行系统研究，以获得稳定性好、探测效率高、能量分辨率优良的平面型及阵列型室温核辐射探测器。

溴化铊（TlBr）是一种非制冷型核辐射探测器用新型宽禁带化合物半导体材料，与GaAs、PbI2、CdZnTe等半导体探测材料相比，TlBr由于其物理特性优良且易于熔融生长等特点成为制备高能射线探测器的热点材料。.该项目通过深入研究TlBr晶体生长动力学及缺陷热力学，结合各种表征手段来优化生长及制备技术，以制备高能射线探测用的完整性好、热应力小、缺陷少的高性能大尺寸TlBr单晶及获得稳定性好、探测效率高、能量分辨率优良的室温核辐射探测器为目标。项目研究内容主要包括单晶的熔体法如垂直温度梯度凝固法和布里奇曼法生长，系统研究了温度梯度、生长速率、安瓿直径等对晶体质量的影响。在获得理想的生长工艺参数的基础上，研究了不同保护气体（如真空、氧气等）及其气压、温度等参数对晶体性能的影响，结合X射线摇摆曲线、EDS能谱、扫描电镜、红外透过、I-V特性测试等手段对晶体质量（包括单晶完整性、光学性能、电学性能、能谱响应等）及缺陷热力学机制进行分析，得出TlBr晶体中的缺陷主要与生长过程中Br空位的产生有关，获得了有效控制晶体化学配比及减少热缺陷的工艺条件。研究了Ti、Au金属电极材料的功函数等对Ti/TlBr/Ti、Au/TlBr/Au探测器中金属-半导体的界面结构的影响及欧姆接触形成的机理；改进并优化了晶片的加工过程、晶片的制备及探测器单元的制作，获得了在241Am放射源59.5keV谱线的照射下能稳定工作的探测器元件。.项目按计划执行,在课题组全体成员的共同努力下，较好地完成了研究目标。通过对晶体的气氛生长与晶体热缺陷的控制、晶片加工及表面处理、晶片的退火改性、欧姆电极的沉积等关键制备工序进行系统研究并优化其工艺参数，提高了晶体质量及探测性能。晶体的电阻率 ≥ 1011cm，且I-V呈现良好的线性性，晶体红外透过率 60%，载流子迁移率寿命积达到10-4数量级，探测器元件对241Am放射源59.5keV谱线的能量分辨率11.8%；掌握了大尺寸单晶的生长工艺参数，获得直径8-15 mm的TlBr晶体及核辐射探测器；取得了一定理论及实际应用价值的成果,对进一步应用研究打下了基础。