硅基原子层厚结构的计算研究

发布时间：2017-12-27 09:35

本文关键词：硅基原子层厚结构的计算研究　出处：《浙江大学》2017年博士论文　论文类型：学位论文

【摘要】：石墨烯、硅烯和锗烯等二维材料的发现引起了人们极大的研究兴趣,这主要是由于其优异的物理性质和广泛应用前景。其中,具有蜂窝状晶格结构的由单层硅原子构成的硅烯因其特殊的性质而成为近年来研究的热点。理论表明具有low-buckled结构的硅烯在电场调控电子结构和与传统的硅基工艺兼容等方面比平面结构的石墨烯更有优势。然而,本征硅烯的零带隙是阻碍其在器件领域应用的主要障碍。本论文在密度泛函理论(DFT)的框架下,研究了氧化、空位、纳米化和杂化结构对硅烯结构、电子和磁学性质的影响,为硅烯的电子结构和性能调控提供理论支持。本论文取得的主要成果如下:(1)研究了银(111)面上氧化的硅烯的形成能、结构和电子性质,考察氧化对银(111)面上硅烯性能的影响。结果表明,氧化会改变银(111)面上硅烯的蜂窝状晶格结构。由于氧化硅烯和银(111)面强烈的耦合作用使氧化硅烯具有金属特性的能带结构。氧化硅烯和银(111)表面之间的电荷积累表明两者形成了化学键和,这会显著影响氧化硅烯的的电子性质。当氧化硅烯从银(111)面上剥离时,它们有可能变成半导体。(2)系统研究了具有不同空位浓度硅烯的形成能、电子和磁学性质,并和石墨烯进行对比。研究发现,硅烯的磁矩随着其中空位浓度的增加而减小。此外,和具有空位的石墨烯相比,具有空位的low-buckled硅烯可能具有更加显著的带隙。随着空位的形成,硅烯会从半金属转变为半导体,而石墨烯会变成金属。(3)研究了不同尺寸氢钝化的黑磷量子点(BPQDs)和黑磷量子点/硅烯杂化结构的电子性质,结果表明黑磷量子点最高占据分子轨道(HOMO)和最低未占据分子轨道(LUMO)之间的带隙随着量子点尺寸的减小而增大,量子点稳定性却随着尺寸减小而减弱。黑磷量子点/硅烯杂化结构的吸附能和带隙随着量子点尺寸的增加而增大。硅烯上吸附P76H22量子点会使硅烯具有102 meV的禁带宽度。电荷转移分析表明电荷从硅烯转移到黑磷量子点,并且转移的电荷量与硅烯表面黑磷量子点的覆盖率有关。(4)研究了 Si6-xCx/C超晶格的电子性质。通过替换石墨烯中的碳原子构建不同硅碳比例的Si6-xCx/C超晶格。结果表明,Si6-xCx/C超晶格在狄拉克(Dirac)处具有直接带隙,其电荷的有效质量为0.016-0.646me。Si6-xCx/C超晶格的带隙强烈地依赖于六元环石墨烯中硅原子的数量和位置。通过PBE交换关联泛函和B3LYP杂化泛函计算得到Si3C3/C超晶格具有最大的带隙,分别为0.3和0.54 eV。对其进一步的研究表明,Si3C3/C超晶格在室温下的载流子迁移率高达1.2854x105cm2V-1s-,其声子热导率为15.48Wm-1K-1。结合传输系数和低声子热导率,通过微调Si3C3/C超晶格中的载流子浓度,可以优化其热点品质因数到1.95。
[Abstract]:The discovery of two-dimensional materials such as graphene, Silene and germanene has attracted great interest, mainly due to their excellent physical properties and wide application prospects. Among them, the Silene, which is composed of monolayer silicon atoms with honeycomb lattice structure, has become a hot spot in recent years because of its special properties. The theory shows that Silene with low-buckled structure has advantages over planar structure graphene in terms of electric field regulation, electronic structure and compatibility with traditional silicon-based process. However, the zero band gap of the intrinsic silicon is the main obstacle that hinders its application in the field of devices. In the framework of density functional theory (DFT), we have studied the effects of oxidation, vacancy, Nanocrystallization and hybrid structure on the structure, electronic and magnetic properties of silylene, providing theoretical support for the electronic structure and property control of silylene. The main achievements of this paper are as follows: (1) the formation energy, structure and electronic properties of silylene on silver (111) surface were investigated, and the effect of oxidation on the properties of silylene on silver (111) surface was investigated. The results show that oxidation will change the honeycomb lattice structure of Silene on the silver (111) surface. Because of the strong coupling effect of Silene and silver (111) surface, the SiO2 has a metal band structure. The charge accumulation between the silicon oxide and the silver (111) surface indicates that both of them form chemical bonds, which will significantly affect the electronic properties of the SiO2. When the silicon oxide is stripped from the silver (111) surface, they may become semiconductors. (2) the formation energy, electron and magnetic properties of Silene with different vacancy concentration are systematically studied and compared with Shi Moxi. It is found that the magnetic moment of Silene decreases with the increase of the vacancy concentration. In addition, the low-buckled Silene with vacant positions may have a more significant band gap compared with the vacant graphene. With the formation of vacancies, Silene will change from semi metal to semiconductors, and graphene will become metal. (3) black phosphorus quantum dots of different sizes of hydrogen passivation (BPQDs) and electronic properties of black phosphorus / silicon quantum dot graphene hybrid structure. The results show that black phosphorus quantum dots of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) gap between the increases with the size of quantum dots the decrease of quantum dots were decreased with decreasing the size and stability. The adsorption energy and band gap of the black phosphorus quantum dot / Silene hybrid structure increase with the increase of the quantum dot size. The adsorption of P76H22 quantum dots on Silene makes Silene with a band gap of 102 meV. Charge transfer analysis shows that the charge transfer from Silene to black phosphorus quantum dots, and the amount of transfer charge is related to the coverage of the black phosphorus quantum dots on the Silene surface. (4) the electronic properties of Si6-xCx/C superlattice are studied. Si6-xCx/C superlattices with different ratios of silicon and carbon are constructed by replacing carbon atoms in graphene. The results show that the Si6-xCx/C superlattice has a direct band gap at Dirac (Dirac), and the effective mass of the charge is 0.016-0.646me. The band gap of the Si6-xCx/C superlattice strongly depends on the number and position of the silicon atom in the six membered ring graphene. The maximum band gaps of Si3C3/C superlattices are obtained by the PBE exchange functional and B3LYP hybrid functional calculations, which are 0.3 and 0.54 eV, respectively. The further study shows that the carrier mobility of Si3C3/C superlattice at room temperature is up to 1.2854x105cm2V-1s-, and its phonon thermal conductivity is 15.48Wm-1K-1. Combining the transmission coefficient and the low sound conductivity, the hot quality factor of the Si3C3/C superlattice can be optimized by fine tuning the carrier concentration in the superlattice, and the quality factor of the hot spot can be optimized to 1.95.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O613.72

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