碳化硅（SiC）是多种低剂量率辐射环境中重要的结构材料和半导体材料。为了利用实验室离子辐照条件模拟材料的真实服役行为以及研究辐照效应机理，不同粒子的辐照等效性问题成为关键的科学和技术问题。为了避免基于核能量沉积的等效模型的缺陷，本论文将等效性问题分解，以微结构作为联系外场条件和性能变化的桥梁，分别研究不同缺陷组态情形下的微结构演化模型以及微结构与性能的相关性模型，并建立描述微结构特征的关键参数以及相应的表征方法。 首先针对离位原子缺陷开展自离子室温辐照实验，并利用卢瑟福背散射沟道谱（RBS/C）和透射电子显微镜（TEM）分析离位原子浓度和缺陷构型的深度分布。结果表明微结构演化由不均匀的类似非晶区域的形核与生长过程以及均匀的晶态-非晶态（c-a）转变构成。对于不同的离子能量可基于平均离位原子数建立统一的离位原子缺陷与力学/光学参数的相关性模型。杨氏模量的三段变化与微结构演化阶段相对应，其中特别反映了c-a转变伴随的弛豫过程的影响。光学带隙和Tauc系数则表现出两段变化，可反映带边缺陷态密度和电子态局域性的演化过程。 然后针对He/空位共存时的复杂缺陷组态开展{\rm He}^+室温/高温辐照和高温退火实验，综合利用可见（Vis）光谱、高分辨率X光衍射（HRXRD）谱和慢正电子湮灭多普勒展宽谱（SPADBS）表征折射率、应变和空位型缺陷的深度分布，并提取折射率相对增量作为序参量。缺陷分析确定了不同He浓度、DPA和温度条件下至少两种起始空位缺陷及其相应的饱和氦泡演化路线、以及极端条件下更大尺寸的不饱和氦泡构型。在多缺陷类型共存的复杂情形中，由于难以直接对缺陷进行定量表征，本论文利用序参量和应变参量建立性态坐标以描述微结构整体特性，其在不同外场条件下的演化形成两条轮廓线，分别对应高失序状态和弛豫状态。基于性态坐标与力学/光学参数的相关性分析，验证了序参量对杨氏模量的影响和Tauc系数的序参量本质，并在特定的辐照和退火路线上建立了杨氏模量随应变变化率与序参量随应变变化率的关系曲线。 最后，针对电学性质对辐照剂量的高敏感度开展更低剂量辐照实验，利用与衬底绝缘的n型外延层上的圆形传输线欧姆电极结构分析得到了SiC电导率的指数衰减规律，同时观察到欧姆接触电阻率的增加及其向整流接触的转变。
Silicon carbide (SiC) serves in a variety of low dose rate radiation environments as an important structural material and semiconductor material. With the use of laboratory ion irradiation to simulate practical radiation effects and help study relevant physical mechanisms, the equivalence between different particles has become a key scientific and technical problem. In order to avoid the limitations of the equivalence model based on nuclear energy deposition, this paper splits the equivalence problem and considers microstructure as the linking bridge between external-field conditions and property variation, aiming to study respectively the evolution model of microstructure and the correlation model between microstructure and macro-property under various defect configurations, at the same time establishing key parameters and corresponding characterization methods to describe the microstructure characters. Firstly, in order to study the defect of displaced atoms, self-ion irradiation at room temperature (RT) was performed, with Rutherford backscattering spectrum/channeling (RBS/C) and transmission electron microscopy (TEM) used to analyze the depth distribution of defect concentration and configuration. The result shows that microstructure evolution consists of the heterogeneous nucleation and growth of amorphous-like regions and the homogeneous crystalline-amorphous (c-a) transition. Based on the average concentration of displaced atoms, the unified correlation model between microstructure and mechanical/optical properties has been established regardless of ion energies. Young’s modulus experiences three variation stages in correspondence with microstructure evolution, specifically exhibiting the effect of the relaxation process accompanying the c-a transition. The variation of optical bandgap and Tauc coefficient shows two stages, which reflects the evolution of near-gap state density and electron state localization. Secondly, in order to study the complex defect configuration where He/vacancy coexist, {\rm He}^+ irradiation at RT/high temperature and subsequent high temperature annealing were conducted. Three methods including Visible spectrum, high-resolution X-ray diffraction (XRD) spectrum and slow positron annihilation Doppler broadening spectrum (SPADBS) were used to analyze the depth distribution of refractive index, strain and vacancy-type defect configurations, and the relative increment of refractive index was considered as the order parameter. Defect analysis identifies at least two vacancy types and their corresponding evolution routes towards saturated helium bubbles under different He concentration, DPA and temperature conditions, as well as one larger unsaturated helium bubble configuration under more extreme conditions. Because it’s difficult to directly perform quantitative characterization on defects under such complex situation where various defect types coexist, this paper establishes character coordinates with order parameter and strain parameter to describe the overall microstructure character instead, whose evolution under different external-field conditions forms two contour lines, corresponding to high disorder state and relaxation state respectively. Based on the correlation analysis between character coordinates and mechanical/optical parameters, the influence of order parameter on Young‘s modulus is observed, and Tauc coefficient is verified to be an order parameter as well. For specific irradiation and annealing process, the relationship between the variation rate with strain of Young‘s modulus and order parameter has been established. Finally, in view of the high sensitivity of electrical properties to radiation dose, the very low dose irradiation experiments were carried out. By preparing ohmic electrodes with the structure of circular transmission line on the n-type epitaxial layer insulated from the substrate, the electrical conductivity of SiC was analyzed and shows exponential attenuation with DPA. At the same time, the increase of specific contact resistivity and the transition from ohmic contact to rectified contact were observed.
