氢钝化4H-SiC（0001）表面本征点缺陷及其吸附金属（Ag、Mo）后的结构与电子性质理论研究

发布时间：2018-03-13 05:28

本文选题：碳化硅　切入点：氢钝化表面　出处：《江苏大学》2017年硕士论文　论文类型：学位论文

【摘要】：碳化硅(SiC)是一种物理化学性质优良、应用前景广阔的的宽禁带半导体材料。无论是作为结构材料还是功能材料,SiC表面的结构及其相应的物理化学性质对其在诸多领域的应用至关重要,特别是氢钝化的4H-SiC(0001)表面,由于其在新一代电子器件以及二维纳米薄膜制备领域独特的优势,对其表面的微观结构、状态以及物理化学性质进行原子尺度的深入探索显得尤为重要。本研究基于第一性原理计算,从原子尺度系统研究了七种代表性的点缺陷(包括ISi、IC、VSi、VC、CSi、SiC、CSiSiC)对氢钝化的4H-SiC(0001)表面结构的影响,并系统考察了这几类表面缺陷与两种常用表面改性金属原子(Ag、Mo)之间的相互吸附作用以及对表面电子能带结构的影响。具体内容和结论如下:首先,我们计算了位于氢钝化4H-SiC(0001)面的七种点缺陷的形成能和微观结构,细致考察了以上点缺陷随着深度变化对近邻晶格变形的影响程度,并分析晶格变形与形成能之间的关系,从而系统比较以上缺陷分别在4H-SiC体相、理想(0001)表面和氢钝化(0001)表面的形成能大小关系及相应的热力学稳定性。此外,我们分别研究了晶胞大小、化学势对点缺陷形成能的影响,并根据形成能大小估算了这些缺陷的在不同温度下的热力学浓度。结果表明,填隙缺陷的结构在氢钝化面是不稳定的。除了碳填隙缺陷和碳空位缺陷,其他缺陷的形成能随层数的增加而增加。而且除反位缺陷,其他缺陷的形成能比体内缺陷的形成能低,但是比理想表面的形成能高。其次,通过计算结合能,我们比较了氢钝化4H-SiC(0001)表面不同点缺陷对两种金属原子(Ag、Mo)吸附性强弱,并结合二次差分电荷密度对其相互作用下的电荷转移及成键情况进行了细致的表征分析,揭示了其相互作用强弱差异的主要原因,同时在理论上解释了SiC表面金属离子注入后,其表面金属化以及表面润湿性提高的微观物理机制。计算结果表明,与无缺陷的氢钝化表面相比,带有悬挂键的点缺陷(如空位、填隙原子)能够显著提高对Ag(Mo)的吸附性能。其最高吸附性能提高比例分别高达4150%(238.1%)。另外,通过电子能带和态密度计算,我们分析比较了点缺陷以及吸附金属原子对氢钝化4H-SiC(0001)表面的电子性质的影响。结果显示,对(0001)表面进行氢钝化能够消除理想表面的附加能级,使得导带底和价带顶上移。表面点缺陷以及吸附的金属能够在禁带区域引入附加能级,其中以深能级为主。金属Ag(Mo)的吸附能够增加体系的磁矩,并且吸附Mo引入的附加能级数目多于Ag。
[Abstract]:Sic is a kind of excellent physical and chemical properties. The structure of sic surface and its corresponding physical and chemical properties are very important for its application in many fields, especially the hydrogen passivated 4H-SiCn0001 surface, which is widely used as a wide band gap semiconductor material, both as a structural material and as a functional material, and its corresponding physical and chemical properties are very important for its application in many fields, especially the hydrogen passivated 4H-SiCn001 surface. Due to its unique advantages in the new generation of electronic devices and the preparation of two-dimensional nanocrystalline films, It is very important to explore the state and physicochemical properties at atomic scale. The effects of seven representative point defects (including ISi-ICVSi-VSi-CSi-CSiC- CSiC- CSiCon) on the surface structure of hydrogen-passivated 4H-SICP _ (0001) have been studied by atomic scale system. The interaction between these kinds of surface defects and two commonly used surface modified metal atoms (Ag-Mo) and their effects on the surface electronic band structure are also systematically investigated. The specific contents and conclusions are as follows: first of all, We have calculated the formation energy and microstructure of seven kinds of point defects located on the hydrogen passivated 4H-SiCn0001) surface. We have carefully investigated the influence of the above point defects on the lattice deformation of the nearest neighbor with the change of depth, and analyzed the relationship between the lattice deformation and the formation energy. Therefore, the relationship between the formation energy and the thermodynamic stability of the above defects on the 4H-SiC, ideal and hydrogen passivated surfaces are systematically compared. In addition, the effects of the cell size and the chemical potential on the formation energy of the point defects are studied respectively. The thermodynamic concentration of these defects at different temperatures is estimated according to the formation energy. The results show that the structure of the interstitial defects is unstable on the hydrogen passivation surface, except for the carbon filling defects and the carbon vacancy defects. The formation energy of other defects increases with the increase of the number of layers. Besides, the formation energy of other defects is lower than that of internal defects, but higher than that of ideal surface. Secondly, the binding energy is calculated. In this paper, we compare the adsorption of two kinds of metal atoms with different defects on the surface of hydrogen passivated 4H-SiO _ (0001), and analyze the charge transfer and bond formation under the interaction of the two metal atoms by combining with the secondary differential charge density. The main reasons for the difference of interaction are revealed, and the microphysical mechanism of surface metallization and surface wettability improvement after metal ion implantation on SiC surface is theoretically explained. In comparison with non-defect hydrogen passivated surfaces, point defects with hanging bonds (such as vacancies, interstitial atoms) can significantly improve the adsorption properties of Agnimo. The highest adsorbability can be increased by up to 4150% and 238.1%, respectively. By calculating the electron band and the density of states, we have analyzed and compared the effects of point defects and adsorbed metal atoms on the electronic properties of the hydrogen passivated 4H-SiCn0001) surface. The results show that hydrogen passivation on the surface can eliminate the additional energy level on the ideal surface. The surface defects and the adsorbed metals can introduce additional energy levels in the gap region, in which the deep level is the main energy level. The adsorption of the metal AgMoMo can increase the magnetic moment of the system. The number of additional energy levels introduced by adsorption Mo is more than that of Ag.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O647.3;TQ163.4

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