第一性原理对Bi系材料结构特性及应用的模拟研究

发布时间：2018-04-28 00:17

本文选题：Bi系材料 + 能带结构　；参考：《中国矿业大学》2015年硕士论文

【摘要】：Bi2X3(X=Se,Te,S)是VB-VIB族中三种重要的半导体材料,具有一系列优异的特性。本文通过第一性原理系统化地研究了这三种材料块体、薄膜和表面及相关结构掺杂的电子结构,对其晶体结构和由晶体结构变化导致的电子结构变化有了一定程度的研究。本文的主要研究内容包括:首先,对R-3m结构Bi2Se3材料的电子结构进行了计算分析,结果表明:其纯净块体为直接带隙半导体,带隙值约为0.32e V,与实验值吻合较好,Se原子和Bi原子的p轨道态,构筑了它们的价带和导带;单“五层”(quintuple layer,QL)薄膜表现出间接带隙特性,带隙值约为0.91e V,态的构成与块体类似;掺入Pb后,与Pb近邻的Se(1)层原子排列发生变化,变为Se(1/)层,Pb掺杂对能带结构的影响主要是通过Se(1/)层来实施的,其自身原子态的影响有限;Bi的6s态对价带顶有调制作用,该调制使得块体保持直接带隙半导体的特征;而对于薄膜,Bi的6s态的对价带顶处态的影响显著降低,这时的弱调制导致它们的价带顶偏离导带底位置,带隙的性质也从直接带隙变化为间接带隙;单QL薄膜同样表现出间接带隙特性,带隙值约为0.24e V,其价带和导带主要由p态构成,掺杂Al原子后带隙表现出11.5%的降低,态的构成并未发生重大调整;平面应变下薄膜电子结构的变化,主要体现在带隙值随应变比例的线性改变。其次,对R-3m结构Bi2Te3材料电子结构进行了计算分析,结果表明:Bi2Te3块体材料和Bi2Se3类似,表现出直接带隙特征,带隙值约为0.177e V,计算结果表明自旋轨道耦合作用对电子结构无重大影响。而单QL薄膜表现出明显的间接带隙特征,带隙值约为1.031e V。双QL薄膜相较于单QL薄膜其间接带隙特性减小,带隙值约为3.122e V;平面应变下薄膜电子结构的变化,主要体现在带隙值随应变比例的线性改变,不同厚度薄膜斜率不同。最后,对Bi2S3材料的电子结构进行了计算分析,结果表明:Pnma结构Bi2S3块体属于间接带隙半导体,但价带顶位置不明显,带隙值约为1.198e V;Bi2S3块体中在掺杂Se、Te后电子结构未有太大变化,主要是由于掺杂原子与S原子性质近似,其带隙值分别为1.186e V和1.001e V,差别主要来自于不同原子对周期性势场调整的不同;而Bi2S3(R-3m结构)块体表现出直接带隙特征,带隙值约为1.046e V,这也为实验上的探索提供了参考。
[Abstract]:Bi2X3 XSe TeSs is one of the three important semiconductor materials in the VB-VIB family, which has a series of excellent properties. In this paper, the doped electronic structures of these three kinds of bulk materials, thin films, surfaces and related structures have been systematically studied by first principles. The crystal structure and the electronic structure changes caused by the crystal structure changes have been studied to a certain extent. The main contents of this paper are as follows: firstly, the electronic structure of R-3m Bi2Se3 material is calculated and analyzed. The results show that the pure bulk is a direct bandgap semiconductor. The band gap value is about 0.32e V, which is in good agreement with the experimental values of p orbital states of se atom and Bi atom, and their valence band and conduction band are constructed, while the single "five layers" quintuple layer QLL film exhibits indirect band gap characteristics, the band gap value is about 0.91e V, and the composition of the state is similar to that of the block. After the addition of Pb, the atomic arrangement of the adjacent Sean1 layer of Pb changed, and the effect of Pb doping on the energy band structure was mainly carried out by the Se1 / 1) layer. The influence of its own atomic state on the valence band top was limited by the 6s state of Bi. The modulation enables the bulk to retain the characteristics of direct band gap semiconductors, while the effect on the valence band top states of the 6s state of the thin film Bi decreases significantly, and the weak modulation results in their valence band top deviating from the bottom of the conduction band position. The properties of the band gap also changed from the direct band gap to the indirect band gap, and the band gap value of the single QL thin film was about 0.24 EV, the valence band and the conduction band were mainly composed of p states, and the band gap after doping Al atoms showed a decrease of 11.5%. The changes of electronic structure of the thin film under plane strain are mainly reflected in the linear change of band gap value with strain ratio. Secondly, the electronic structure of R-3m Bi2Te3 material is calculated and analyzed. The results show that the ratio Bi2Te3 block material is similar to Bi2Se3 and shows direct band gap characteristics. The band gap is about 0.177e V. the calculated results show that the spin-orbit coupling has no significant effect on the electronic structure. However, the single QL thin films exhibit obvious indirect band gap characteristics, with a band gap value of about 1.031 EV. Compared with single QL thin films, the indirect band gap characteristics of double QL thin films are reduced, the band gap value is about 3.122 EV, and the electronic structure of double QL thin films under plane strain is mainly reflected in the linear change of band gap value with strain ratio, and the slope of different thickness films is different. Finally, the electronic structure of the Bi2S3 material is calculated and analyzed. The results show that the Bi2S3 block is an indirect band gap semiconductor, but the valence band top position is not obvious. The band gap value is about 1.198 e / v ~ (2) Si _ (2) S _ (3). The main reason is that the doped atom is similar to the S atom, its band gap values are 1.186e V and 1.001e V, respectively, the difference mainly comes from the difference of the adjustment of the periodic potential field between the different atoms, while the Bi2S3(R-3m structure) block shows the direct band gap characteristic, and the band gap value of the doped atom is 1.186e V and 1.001e V, respectively. The band gap value is about 1.046 EV, which provides a reference for experimental exploration.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN304

【参考文献】