【作者】 徐新发；

【导师】 邵晓红；

【作者基本信息】 北京化工大学 ， 凝聚态物理， 2009， 硕士

【摘要】 SrTiO₃是一种钙钛矿金属氧化物绝缘体,它被广泛用于晶界电容器、氧敏传感器、光开关、生长高温超导薄膜的衬底,作为高电容率材料在超晶格和下一代超大规模集成器件中具有潜在的应用价值。目前,对SrTiO₃电子结构、半导化掺杂、导电模型、缺陷态、表面/界面态等方面已有了不少的理论和实验研究。其中对于n型掺杂前人研究较多,对于p型掺杂和各种空位缺陷研究较少。本文采用基于密度泛函理论框架下的第一性原理软件VASP,对SrTiO₃材料的电子结构、本征缺陷、掺杂改性进行研究,所用软件为VASP（Vienna Ab-initio Simulation Package）软件包。主要研究内容及结果如下:一、系统地计算了SrTiO₃几何和电子结构,包括晶体结构、能带结构、态密度。计算结果表明SrTiO₃是一种间隙半导体。比较总态密度和各原子得分波态密度可知,价带顶（R点）电子主要由O 2p态电子提供,导带底（г点）电子主要由Ti 3d提供。二、系统地计算了不同空位浓度下SrTiO_3-x,Sr_1-xTiO₃和SrTi_1-xO₃（X=0.125,0.25,0.33）的几何结构和电子结构,包括晶格常数,能带结构、态密度、分波态密度。结果表明:通过引入O空位,使体系费米能级进入导带中。并且随着空位浓度的增大,进入到导带中的位置越深,属于n型掺杂,在禁带中产生了缺陷能级;引入Sr空位或Ti空位后,体系的费米能级进入到价带中,并且随着空位浓度的增大,进入到价带中的位置越深,属于p型掺杂,在价带项附近引入了缺陷能级。三种空位的引入,都使体系从绝缘性向金属性转变,其中Ti空位对体系导电性改善效果最好。三、研究了不同掺杂浓度替位掺杂对SrTiO₃几何结构和电子结构的影响。结果显示Y替位Sr掺杂属于n型掺杂,体系Sr_1-xY_xTiO₃（X=0.125,0.25,0.33）的费米能级进入导带中,在导带底出现大量由掺杂原子贡献的自由载流子-电子,明显提高了电导率,改善了SrTiO₃的导电性能。In或Al替位Ti掺杂为p型掺杂,体系SrTi_1-xIn_xO₃(SrTi_1-xAl_xO₃)（X=0.125,0.25,0.33）的费米能级进入价带中,掺杂在价带顶附近引入缺陷能级,费米能级处电子态密度不为零,从而使得体系的导电能力增强。三种情况下的掺杂都使体系转变为金属性,其中Y替位Sr对体系导电性改善效果最好。更多还原

【Abstract】 As a typical perovskite material, strontium titanate （SrTiO₃） has been widely used in oxygen-gas sensor, optical switch, epitaxial growth substrate fields. It has potential application in superlattice and large-scale integration fields for its high permittivity. At present, much theoretical and experimental investigations of SrTiO₃ have been carried out on electronic structure, doping, conductivity model, defect states, surfaces and interface of SrTiO₃. Among the researches, much focus on n-type doping and there is little study on the p-type doping and vacancy defect. The first principle package （VASP） based on the density functional theory （DFT） is used to study the n-type doping, electronic structures, intrinsic oxygen vacancies, strontium vacancies and titanium vacancies. The main contents are as the following:1. The detailed investigations have been carried out, including the geometry and electronic structure, crystal structure, band structure, density of states （DOS） and sub-wave density of states of SrTiO₃ in the cubic phase. The results show that SrTiO₃ is indirect band gap semiconductor. The valence band top was at the point of R and the electrons are supplied by 2p state of oxygen atom, while the bottom of conduction band was at the point ofΓand the electrons are supplied by 3d state of titanium atom.2. The geometry and electronic structure calculations of SrTiO_3-x, SrTiO_3-x and SrTi_1-xO₃（X=0.125, 0.25, 0.33） were investigated. Due to the O vacancy electron doping, the Fermi level moves into CBs and the position got deeper while the doping concentration increased. The defect band level appeared in the forbidden band as a result of the O vacancy. Due to the Sr vacancy or Ti vacancy cavity doping, the Fermi level moves into VBs and the position was deeper while the doping concentration increased. The defect band level appeared at the top of valence band as a result of the Sr vacancy （or Ti vacancy）. So by introducing one of the three types of vacancy, the system shows metallic behavior.3. Both n-type and p-type doping for SrTiO₃ were carried out. The results show that strontium atom substituted by yttrium atom was n-type doping. The Fermi level of Sr_1-XY_XTiO₃ （X=0.125, 0.25, 0.33） moves into CBs and there are lots of free electrons provided by the impurity atoms in the bottom of conduction band and the conductivity of SrTiO₃ is well improved. While indium or aluminum substituted titanium was p-type doping. The Fermi level of SrTi_1-XIn_XO₃(SrTi_1-xAl_XO₃)（X=0.125, 0.25, 0.33） moves into VBs and the defect band appeared upon the top of valence band. So the conductivity of the system is enhanced. In conclusion, the system shows metallic behavior by the three types of doping.更多还原