导　　师： 王松有;陈良尧;郑玉祥;李晶;张荣君

学科专业： 070207

授予学位： 硕士

作　　者： ;

机构地区： 复旦大学

摘　　要： 本论文利用基于密度泛函近似的第一性原理方法,研究了三种材料的电子结构和光学性质。本论文主要包括以下几方面的内容： 首先,本文采用局域自旋密度近似/(LSDA/)的第一性原理方法计算了直接带隙红外材料Hg1-xCdxTe/(MCT/)/(x=0.250,0.375,0.500,0.625,0.875与1.000/)的电子结构和光学性质。MCT材料是目前红外探测领域的领军材料,因其独特的可调带隙宽度、较高的电子迁移率和较宽的应用温度范围等优点,成为了目前研究的热点。在本文的计算过程中,先进行晶格优化,理论计算的该材料的晶格常数符合Vergard定律,随着Hg浓度的增加,线性地减小；其能带结构是相似的,不同组分的材料,主要表现在带隙宽度的差异,价带顶和导带底都在r点；其介电函数虚部主要有三个吸收峰,随着Cd浓度的增加而蓝移,说明该材料的导带随着Cd浓度的升高而升高,导致其带隙宽度增加；其静态介电常数则随着Cd浓度的增加而按照抛物线的规律下降；能量损失谱和有效电子密度的计算结果表明只有很少的价电子参与了带间跃迁。 SnxGe1-x材料是另外一种具有带隙可调和很高的电子迁移率的半导体材料,因此它在光电子应用领域作为一种有前景的替代Ⅲ-Ⅴ族化合物的材料,且能与现有的硅基半导体工艺兼容而引起人们的广泛关注。本文的第二部分采用基于密度泛函理论/(DFT/)的广义梯度近似/(GGA/)方法计算了直接带隙材料SnxGe1-x/(x=0.000,0.042,0.083,0.125,0.167,与0.208/)的电子结构和光学性质。理论计算的晶格常数符合Vergard定律,随着锡浓度增加而增加,与实验数值相符,通过对能带结构的分析表明,SnxGe1-x均是直接带隙半导体,在计算的五种不同锡浓度情况下均为直接带隙,其带隙随着锡浓度的增加而减小,符合实验的抛物线规律；接着计算了该材料的光学性质,其复介电函数有两个主要的吸收峰,用其带间跃迁分析可以解释这两个主要的吸收峰,其能量损失谱表明它的体等离子体共振频率随着锡浓度的增加而降低,其静态介电常数则随着锡浓度增加而增加。这些结果为其实际应用提供了理论指导。 Mg2FeH6是目前已知的所有氢化物中具有最高的体积储氢密度的化合物,而且它相比其它氢化物还具有成本低廉的优势。本文的第三部分采用第一性原理研究了它的电子结构、光学和弹性性质。首先对其晶格进行了几何优化,优化后的晶格常数与实验相符。计算发现Mg2FeH6是直接带隙半导体,与实验相符,其带隙宽度为1.94eV；在此基础上计算了它的介电函数,并结合电子结构特性,分析了其光学吸收的性性质；能量损失谱在57.35eV处有一个尖锐的峰,表明其体等离子体共振频率为57.35eV；最后本文计算了它的弹性常数、杨氏模量和泊松比。 This thesis presents the fundamental of the computational materials science and its primary research methods, including the ab initio computations and the molecular dynamics simulations, as well as the theoretical way to obtain the structural properties, the mechanic properties, and the optical properties of the crystal and the non-crystal materials. The thesis is arranged as the following parts: First, the electronic structures and optical properties of the direct-band-gap alloys Hg1-xCdxTe /(x=0.250,0.375,0.500,0.625,0.875 and 1.000/) were calculated with local spin density approximation /(LSDA/) based on density functional theory /(DFT/). MCT alloys are the leading material on infrared detection and it has been the critical point for research because of its unique advantages of tunable band gaps, high electronic mobility, and wide temperature adaptation. The lattice optimization was performed at first and the results satisfy the Vergard's law. With the increase of Cd, the lattice constant decreases linearly. There are similar band structures with only different band gaps in different Cd density alloys and the valence top and conduction bottom are both onΓpoint. There are three main absorption peaks for the dielectric function making blue-shift with the increase of Cd, indicating that the conduction band of the alloy lifting as Cd density increases leading to the band gap increasing. The static dielectric function decreases satisfying a parabolic equation with the increase of Cd. The calculation results of the energy loss function and effective electronic density indicate that there are only few electrons taking part in the interband transition. SnxGe1-x is another material with tunable band gap and high electronic mobility. Therefore it is a prospective candidate to replace theⅢ-Ⅴcompounds in the realm of optoelectronics. Moreover since the material can be compatible to current Si based technology, it is widely interested. In the second part of the paper, the electronic structures and optical properties of the direct band alloys SnxGe1-x /(r=0.000,0.042, 0.083,0.125,0.167, and 0.208/) were calculated using the generalized gradient approximation /(GGA/) based on the density functional theory /(DFT/). The theoretical lattice constants that increase with the increase of Sn are in consistence with the Vergard's law and the experimental values. The band structures show that the materials are the direct band gap semiconductor for the specific five Sn intensities and the band gap decreases with the increase of Sn satisfying the experimental parabolic equation. Then the optical properties of the alloys were calculated and the dielectric function has two main peaks that can be interpreted with the interband transition. The results of the energy loss function tell that the bulk plasma frequency decreases with the increase of Sn but the static dielectric constant increases as Sn increases. The results give conduction to the application of the material. Mg2FeH6 is the hydride with the highest hydrogen volume storage and the lowest cost amongst all hydrides. The third part of the paper introduces its electronic structure, optical and elastic properties results performed using the first-principles calculations. The lattice optimization was performed at first in consistence with the experimental one. It indicated that the crystal is the direct-band-gap material with the band gap of 1.94eV in accordance with the experiment. After that, the dielectric function was calculated and analyzed based on the electronic structure. There is a sharp peak at 57.35eV on the energy loss function, where is the bulk plasma frequency. The elastic constants, Young's modulus, and Poisson's ratio were calculated at the end of the part.

关 键 词： 第一性原理 电子结构 光学性质 弹性常数

分 类 号： [O482.3]

领　　域： [理学] [理学]