纳米氮化硅掺杂体系的第一性原理及分子动力学的模拟研究

发布时间：2017-12-26 19:03

本文关键词：纳米氮化硅掺杂体系的第一性原理及分子动力学的模拟研究　出处：《兰州理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：随着微电子行业的飞速发展,基础器件的特征尺寸又在不断缩小,而传统的脆性陶瓷不能满足其使用要求,成为制约该技术发展的瓶颈,寻求高性能陶瓷是解决此问题的有效途径之一。纳米氮化硅陶瓷具有优异的力学、电学和光学性能,正广泛应用于大规模集成电路及基础器件中,但是,目前大多数的研究主要集中在纳米线、棒、带的合成,对其电学和力学性能缺乏描述,也很难对其进行性能考察与评估。因此,本文利用第一性原理模拟对铟掺杂氮化硅体系进行电子结构和光学性能的研究,采用分子动力学模拟计算氮化硅纳米线的拉伸力学行为进行考察,为纳米氮化硅的设计和控制提供一些有用的参考依据。(1)利用空间群、晶格参数等建立了氮化硅单胞模型,首先对其进行能量最小化弛豫,得到稳定的构型,并与文献相比较;然后建立超晶胞模型,利用一个铟原子取代一个硅原子实现掺杂;最后进行优化计算,获得最佳平衡构型。(2)铟掺杂体系前后带隙分别为4.5和2.1,说明掺杂元素对禁带宽度的影响较大;对于In掺杂体系,一共有81条能带,密度大大增加,下价带28条位于-18~-12电子伏之间,上价带位于-10~0电子伏之间,导带位于3~8电子伏之间;下价带主要来自于In的5s轨道电子和N的2s轨道电子的贡献,顶价带主要来源于N的2p和Si的2p轨道电子的贡献,导带主要来于Si的2p轨道和In的5s轨道电子的贡献。(3)计算的差分电荷密度说明铟掺杂后蓝色区域面积降低,也就是说电子缺失减小了,表明In与N成键的共价性有所降低;计算的布居值从0.65降低到0.35,说明共价性降低了,这与差分电荷密度的结果相一致。计算的介电常数虚部在低能区有所升高,说明介电损耗增大,在低能区寿命降低。(4)在紫外光范围(80-400nm)内,掺杂前后体系对光的吸收都很强,且反射程度高,展示出“阻碍类型”的特点;在可见光区域(400-800nm)内,掺杂前后体系都具有低的吸收和反射谱,说明具有“穿透类型”的特点,也表示光更容易传播。此外,铟掺杂体系在低能区反射谱升高,说明一部分光被反射了。(5)对长径比分别为4:1、6:1和8:1的氮化硅纳米线进行了拉伸加载模拟,随着应变的增加,应力先增加后平缓,应力应变呈现出准线性-非线性关系,弹性极限都约为0.02处;长径比增加,断裂强度降低,峰值应力分别为32.61GPa、31.8GPa和31GPa,长径比的改变显著影响了纳米线的断裂行为。(6)利用可视化软件对不同长径比纳米线的加载过程截取了不同应变点的快照,发现长径比4:1和8:1的纳米线发生断裂的位置位于中心,而长径比为6:1的纳米线发生断裂的位置偏向右端。(7)在加载过程的初期,纳米线内部出现部分Si-Si键缺陷和个别氮原子缺陷;当引发断裂时,在应变约0.048时,Si-Si键缺陷和氮原子缺陷的数量大大增加了,而且出现了新的配位数为0、1和2的氮原子缺陷和配位数为5、6和7的硅原子缺陷,大大加剧了应力集中。
[Abstract]:With the rapid development of the microelectronics industry, the characteristic size of the basic devices is shrinking. The traditional brittle ceramics can not meet the requirements of their applications, and become the bottleneck restricting the development of the technology. Searching for high-performance ceramics is one of the effective ways to solve this problem. Nano silicon nitride ceramics have excellent electrical and optical properties of mechanics, is widely used in large scale integrated circuit and basic devices, but most of the research focused on the synthesis of nanowires, with the rod, and the lack of description of the electrical and mechanical properties, it is very difficult to carry out the inspection and evaluation of its performance. Therefore, this paper using the first principle simulation of electronic structure and optical properties of indium doped silicon nitride system, were investigated by molecular dynamics simulation calculation of tensile behavior of silicon nitride nanowires, provide some useful reference for the design and control of nano silicon nitride. (1) the use of space groups, such as the establishment of lattice parameters of silicon nitride single cell model, the first of its energy minimization relaxation, stable configuration, and compared with the literature; then establish the supercell model, instead of a silicon atom doping using an indium atom; most were obtained after the optimization calculation. The best balance configuration. (2) before and after indium doped system band gap were 4.5 and 2.1, illustrate the influence of doping elements on band gap is relatively large; for the In doped system, a total of 81 bands, the density increases greatly, between the 28 valence band at -18~-12 electron volts, located between -10~0 on valence electron volts, the conduction band located between 3~8 V; 5S electrons and N valence band mainly from the In 2S orbital contribution, the top valence band mainly derived from N 2p and Si 2p orbital contribution, 5S orbital electron conduction band mainly come from Si 2p orbital and In contribution. (3) to calculate the charge density difference shows blue area decreased after indium doping is, electron deficiency reduced, showed that In bond covalency decreased with N; calculating the population decreased from 0.65 to 0.35, indicating covalency is reduced, which is consistent with the charge density difference results. The imaginary part of the calculated dielectric constant increases in the low energy region, indicating that the dielectric loss increases and the lifetime of the low energy region is reduced. (4) in the UV range (80-400nm), absorption of light before and after doping is very strong, and the reflection degree is high, showing the characteristics of "block type"; in the visible light region (400-800nm), before and after doping system has low absorption and reflection spectrum, that has the characteristic of "penetrating type" the light also said more easily spread. In addition, the reflection spectrum of the indium doped system increases in the low energy region, indicating that a part of the light is reflected. (5) the ratio of length to diameter were 4:1, 6:1 And 8:1 silicon nitride nanowires under tensile loading simulation, with the increase of the strain, the stress increased first and then slowly, the stress and strain in quasi linear nonlinear relationship, the elastic limit is about 0.02; the ratio of length to diameter increase, breaking strength decreased the peak stress, respectively 32.61GPa, 31.8GPa and 31GPa, the ratio of length to diameter change has significant influence on the fracture behavior of nano wire. (6) using visualization software to pick up snapshots of different strain points during loading process of nanowires with different aspect ratios, it is found that the fracture location of nanowires located at the center of length and diameter ratio 4:1 and 8:1 is located at the center, while the location of nanowires with the aspect ratio 6:1 is the right side. (7) early in the loading process, the nanowires appear atomic defects Si-Si bond defects and individual nitrogen; when initiating fracture, the strain of about 0.048, the number of Si-Si bond defects and nitrogen atom defects has increased greatly, and appears new defects in silicon atom coordination number is 0, 1 and 2 the nitrogen atom defects and coordination number of 5, 6 and 7, greatly increasing the stress concentration.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ174.1

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