锐钛矿(TiO2)半导体的氧空位浓度对导电性能影响的第一性原理计算

基于低温重氧空位锐钛矿半导体的态密度计算,在同等条件下研究取不同大小模型的锐钛矿做适量浓度的氧空位存在,分别对进入导带的相对平均电子数和氧空位类杂质的散射迁移率进行计算,之后对电导率进行类比,发现锐钛矿半导体的导电性能对适量浓度低的氧空位有利可行得到了证明.同时,低温重氧空位的条件下,锐钛矿半导体的电导率不仅与氧空位浓度有关,而且和进入导带的平均电子数有关,和氧空位散射的电子迁移率有关的正确结论. 关键词： 锐钛矿半导体 氧空位浓度 电导率 第一性原理计算     

高氧空位浓度对锐钛矿TiO2莫特相变和光谱红移及电子寿命影响的第一性原理研究

基于密度泛函理论的第一性原理研究,通过对锐钛矿TiO₂高氧空位浓度、态密度图及吸收光谱图的分析,发现锐钛矿TiO₂高氧空位浓度的条件下,高氧空位浓度对禁带变窄、吸收光谱红移和电子寿命都有很大的影响,从理论上进一步解释了高氧空位浓度对禁带变窄的原因.同时,锐钛矿半导体在高氧空位浓度时发生莫特相变和锐钛矿氧空位在等离子体中吸收光谱红移实验进行比较,发现锐钛矿TiO₂应适量控制高氧空位浓度对吸收光谱红移好于前者.适量控制高氧空位浓度的锐钛矿TiO 关键词： 锐钛矿 高氧空位浓度 吸收光谱红移 第一性原理     

Al-2N高共掺浓度对ZnO半导体导电性能影响的第一性原理研究

采用基于密度泛函理论（DFT）框架下的第一性原理平面波超软赝势方法,在同等环境条件下,建立了不同大小的ZnO模型,在ZnO中对不同浓度的氮和铝原子进行了高掺杂,并对低温条件下高掺杂氮和铝原子的ZnO半导体进行了态密度计算,然后分别对进入价带的相对空穴数和空穴散射迁移率进行了计算,最后对电导率进行了类比,发现适量低浓度的高掺杂氮和铝原子会使ZnO半导体的导电性能增强.即在低温高掺杂氮和铝原子的条件下,ZnO半导体的电导率不仅与掺杂氮和铝原子浓度有关,而且和进入价带的相对空穴数有关.和空穴散射的迁移率有关的结 关键词： ZnO半导体 浓度 电导率 第一性原理     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO2晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法,用第一性原理对含高氧空位浓度的锐钛矿TiO2晶体进行了结构优化处理、能带分布和态密度分布计算,表明在温度一定和高氧空位浓度的条件下,锐钛矿TiO2的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO2晶体中高氧空位浓度时,发现有莫特相变的现象.     

高氧空位简并锐钛矿TiO2半导体电子寿命的第一性原理研究

为了研究锐钛矿TiO₂晶体中高氧空位浓度对电子寿命的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法, 用第一性原理对含高氧空位浓度的锐钛矿TiO₂晶体进行了结构优化处理、能带分布和态密度分布计算, 表明在温度一定和高氧空位浓度的条件下, 锐钛矿TiO₂的电子寿命随氧空位浓度的增大而减小;电子浓度的大小对电子寿命无影响.同时,锐钛矿TiO₂晶体中高氧空位浓度时,发现有莫特相变的现象. 关键词： 高氧空位 2半导体')" href="#">锐钛矿TiO₂半导体 电子寿命 第一性原理     

重氧空位对金红石型和锐钛矿型TiO2导电性能影响的模拟计算

基于密度泛函理论框架下的第一性原理平面波超软赝势方法,构建了未掺杂与相同重氧空位金红石型和锐钛矿型TiO_1.9375超胞模型,分别对模型进行了几何结构优化、能带结构分布和态密度分布的计算. 结果表明,氧空位后金红石型和锐钛矿型TiO₂体系体积均变大,同时,锐钛矿型TiO_1.9375超胞的稳定性、迁移率以及电导率均高于金红石型TiO_1.9375超胞. 计算结果和实验结果相一致. 关键词： 重氧空位 2')" href="#">金红石型和锐钛矿型TiO₂ 导电性能 第一性原理     

ZnO高掺杂Ga的浓度对导电性能和红移效应影响的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,在相同环境条件下建立了浓度不同的由Ga原子取代Zn原子的Zn_1-xGa_xO模型.对低温高掺杂Ga原子的Zn_1-xGa_xO半导体的能带结构、态密度和吸收光谱进行了计算.结果表明:Ga原子浓度越大,进入导带的相对电子数越多,但是电子迁移率反而减小.通过对掺杂和未掺杂ZnO的电导率以及最小间隙带宽度分别进行了比较 关键词： ZnO高掺杂Ga 电导率 红移 第一性原理     

含氧空位锐钛矿TiO2光学性质的第一性原理研究

为了研究锐钛矿TiO2晶体中氧宅位对光学性质的影响,利用基于局域密度泛函理论框架下的广义梯度近似平面波超软赝势方法.用第一性原理对含氧空位锐钛矿TiO2晶体进行了结构优化处理.计算了完整的和含氧空位锐钛矿TiO2晶体的电子态密度、复数折射率、介电甬数及吸收光谱的偏振特性.二者比较发现,引入氧空位后,锐钛矿TiO2的电子结构发生了变化,电子总态密度的费米面进入了导带,引起了莫特相变;含氧空位的锐钛矿TiO2晶体的Ti 3d态大约在-6.097 eV处出现了新的劈裂峰值.两种模型的介电函数虚部、吸收光谱以及复折射率的实部,它们的峰值位置一一对应.说明它们之间存在着内在的联系,这些都与电子态密度分布直接相关.理论分析和计算发现二者的介电函数虚部和吸收光谱峰值位置移动是弛豫效应影响的结果,同时,峰值大小变化是电子跃迁的几率来决定的.晶体的各向异性是由晶体结构的对称性决定的.     

电致发光加速层二氧化硅的电子高场迁移率

根据非晶态半导体的能带理论，讨论了分层优化薄膜电致发光方案中非晶二氧化硅加速层中的电子在高电场中的输运行为.研究结果表明：在高电场下，由于电场的存在降低了陷阱之间的平均势垒高度.在费密能级附近处的杂质及缺陷定域态和导带尾定域态中，电子的输运主要表现为电场增强的热辅助式跳跃传导；而在导带扩展态中，电子的输运仍像晶态半导体那样表现为共有化运动.此外，以实验数据为基础，计算出了非晶二氧化硅中电子的迁移率、最小金属电导率、导带迁移率边界状态密度及费密能级处的状态密度. 关键词：     

Al高掺杂浓度对ZnO导电性能影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法,在同等环境条件下,建立了未掺杂和三种不同浓度的Al原子取代Zn原子的Zn_1-xAl_xO模型,然后分别对模型进行了几何结构优化、总态密度分布和能带分布的计算.结果表明:ZnO高掺杂Al的条件下,随掺杂Al原子浓度增大,进入导带的电子增多,电子迁移率减小,电导率减小,导电性能减弱;但是随高掺杂Al的浓度减小,反而使电子迁移率增大,电导率增大,导电性能增强.计算得到的结果与实验中Al原子 关键词： Al高掺ZnO 电导率 浓度 第一性原理     

Halleffekt und Leitfähigkeitsmessungen an Zinkoxid-Einkristallen mit Sauerstofflücken als Donatoren

The electrical conductivity and Hall effect of pure zinc oxide single crystals have been measured from 5 to 300 K. The temperature dependence of the conductivity and the charge carrier concentration is similar to silicon and germanium. The low temperature conduction mechanism depending on the impurity concentration is explained by means of hopping conductivity and impurity band conduction. The impurity band is supposed to be built up of overlapping wave functions of the excited donor states. The results have been discussed supposing that the donors are oxygen vacancies occupied by one or by two electrons.     

First-principles study of the influences of oxygen defects upon the electronic properties of Nb-doped TiO_2 by GGA + U methods

The influence of oxygen defects upon the electronic properties of Nb-doped TiO2has been studied by using the general gradient approximation(GGA)+U method. Four independent models(i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site(NbTi), an anatase cell with a Nb-dopant and an oxygen vacancy(NbTi+VO), and an anatase cell with a Nb-dopant and an interstitial oxygen(NbTi+Oi)) were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calculated. The results show that in the NbTi+VOcell both eg and t2glevels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies(VO) collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi+Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.     

Origin of semiconductng behavior in rare-earth-doped barium titanate

New explanations of the origin of semiconduction and a peculiar characteristics of resistivity vs dopant concentration in rare-earth-doped barium titanate are presented on a basis of the combined data of cation vacancy concentration, resistivity, and oxygen diffusion coefficient of the material. A limited amount of rare-earth doping into barium titanate results in the introduction of Ba-site vacancies as well as Ti-site vacancies in the lattice. The existence of Ba-site vacancies profoundly alters the chemical bonding nature of the host lattice and thereby causes some loss of oxygen as well as the formation of oxygen vacancies with captured electrons in the lattice on firing the material at elevated temperatures, the latter giving rise to n-type semiconduction. A sudden fall in conductivity for a higher rare-earth concentration occurs in accordance with the number of Ba-site vacancies being zero.     

Halleffekt-messungen an reinen und kupfer dotierten zinkoxidkristallen

The electrical conductivity and Hall effect of pure and copper doped crystals have been measured from 5 to 300 K. The results have been interpreted in terms of high compensation of the donors. Crystals heated in vacuum at 1500 K show impurity band conduction at low temperature. The behaviour of the crystals can be understood by means of oxygen vacancies occupied by one or by two electrons.     

Study on the electronic structures of the reduced anatase TiO2 by the first-principle calculation

Employing the first-principle calculations based on the density functional theory (DFT) and the Molecule Orbital theory (MO), we have researched the electronic structures of the reduced anatase TiO₂ and its visible light photoactivity. The study is emphasized on the O vacancy, including the components of the defect states, the relationship with the bulk states and the way in which these electrons occupying the defect states are distributed in the real space. We find that the origin of the visible light photoactivity should be due to the transition of the excited electrons from the defect states σ_g orbital to the σ_u orbital in the upper conduction bands, rather than arising from the reduction of the band gap. The calculated results indicate that the localized defect states induced by the neutral and doubly ionized oxygen vacancies are all located in the band gap.     

Origins of coexistence of conductivity and transparency in SnO(2)

SnO2 is a prototype "transparent conductor," exhibiting the contradictory properties of high metallic conductivity due to massive structural nonstoichiometry with nearly complete, insulator-like transparency in the visible range. We found, via first-principles calculations, that the tin interstitial and oxygen vacancy have surprisingly low formation energies and strong mutual attraction, explaining the natural nonstoichiometry of this system. The stability of these intrinsic defects is traced back to the multivalence of tin. These defects donate electrons to the conduction band without increasing optical interband absorption, explaining coexistence of conductivity with transparency.