Mg、Ge、Te、Zn掺杂LiFePO_4电子结构的第一性原理计算

本文采用第一性原理研究了Mg、Ge、Te、Zn掺杂的LiFePO_4的能带结构、总态密度以及分态密度.研究结果显示:Mg、Ge、Te、Zn掺杂的LiFePO_4的带隙低于本征体系,有利于电子的跃迁.本征LiFePO_4的能带与掺Mg、Ge、Te、Zn体系带隙之差分别为0.04 e V,0.263 e V,0.691 e V,1.251 e V,说明掺杂Mg、Ge、Te、Zn能够有效的对其能带实现精确调控.在费米能级处,Mg、Ge、Te、Zn掺杂LiFePO_4的态密度主要由Fe的d轨道贡献.     

链间耦合对聚乙炔多链体系中电子极化子再激发态的影响

采用拓展紧束缚Su-Schrieffer-Heeger(SSH)模型,研究了链间耦合对反式聚乙炔多链体系中电子极化子再激发态的晶格位形、净电荷密度、局域能级波函数和态密度的影响.结果发现:对于两条链体系,当链间耦合很小(t⊥≤0.01 e V)时,注入到系统中的电子只会在第一条链上诱发产生一个晶格缺陷,形成电子极化子再激发态,这和单链体系是一致,而第二条链仍是二聚化基态.随着链间耦合的增大,第一条链上缺陷的局域度减少而第二条链上的缺陷局域度相应增加,直至两条链上的位形相同;对于多条链(5条链和6条链)体系,当耦合很小(t⊥≤0.05 e V)时,电子极化子再激发态也只会存在于一条链上,当链间耦合较强时,极化子再激发态会在链间层次性地扩展开来,并不会出现多条链位形相同;从两条链的能级图上可以看到随着链间耦合t⊥的增大,体系的带隙不断的增大和电子态密度显示的是完全吻合的,体系的导电性减弱.通过分析两条链体系在t⊥=0 e V和t⊥=0.1 e V的能级态密度,发现链间耦合越强,则中间局域能级的态密度越小,最后没有中间局域态.     

Mg、Ge、Te、Zn掺杂LiFePO4电子结构的第一性原理计算

本文采用第一性原理研究了Mg、Ge、Te、Zn掺杂的LiFePO4的能带结构、总态密度以及分态密度. 研究结果显示：Mg、Ge、Te、Zn掺杂的LiFePO4的带隙低于本征体系,有利于电子的跃迁.本征LiFePO4的能带与掺Mg、Ge、Te、Zn体系带隙之差分别为0.04 eV,0.263eV,0.691eV,1.251eV, 说明掺杂Mg、Ge、Te、Zn能够有效的对其能带实现精确调控.在费米能级处,Mg、Ge、Te、Zn掺杂LiFePO4的态密度主要由Fe的d轨道贡献.     

Lal-xTexMnO3晶格结构的X射线粉末衍射分析

通过X射线粉末衍射数据,用Rietveld精修方法分析了Te部分替换LaMnO3中La后,其晶格参数及其结构对称性所发生的变化.结果表明:Te掺杂LaMnO3系列样品具有R(3)C的晶格结构对称性,其MnO6八面体晶格还产生了伸张畸变,畸变程度随Te掺杂量的增加而增大.此外根据Mn-O-Mn键角、eg电子能带的带宽、A位离子平均半径及A位离子尺寸失配度等的变化特点,推测Te掺杂LaMnO3样品除居里温度等相变物理量将随x增加而非线性变化外,还可能产生自旋玻璃态、相分离等宏观现象.     

硅酸锌的电子结构

采用局域密度泛函理论和第一性原理的方法,计算四方结构和六角结构硅酸锌的平衡晶格常数、电子态密度和能带结构。计算结果表明,四方结构硅酸锌的平衡晶格常数为0.71048nm,六角结构为1.40877nm,两者与实验值的误差均在1%左右。态密度图显示,主要电子态分布在-7.18～0.00eV和2.79～10.50eV两个能量区域;同时,不同元素电子对导带和价带有不同贡献,其中氧的p态电子对价带顶贡献最大,锌的s态电子对导带底贡献最大。能带计算表明,四方与六角结构硅酸锌均为直接带隙半导体,禁带宽度分别为2.66,2.89eV。     

掺杂ZnTe对电子结构与磁性质的影响

为了研究Mn、Fe、Co、Ni掺杂ZnTe的电子结构和磁性的相关性质.本文基于第一性原理的数值基组的方法计算了Mn、Fe、Co、Ni掺杂ZnTe的能带结构、态密度,分析了掺杂结构的稳定性和磁性性质.结果发现Mn、Fe、Co、Ni掺杂ZnTe的杂质替换能分别为-1.14 e V,-1.23 e V,39.95 e V,-4.32 eV,表明Mn、Fe、Ni掺杂的ZnTe在实验上较容易实现.Mn、Co掺杂ZnTe导致体系产生的总磁矩分别为0.997μB,1.103μB,其中磁性的主要来源于Mn、Co原子在Zn位的取代而引起,产生局域磁性主要取决于Mn、Co的d轨道与Te的p轨道耦合作用.     

高压下ZnTe的电子结构和光电性质

应用第一性原理平面波赝势计算方法,研究了闪锌矿ZnTe晶体在外界压力下的电子结构和光电性质,并计算了介电函数和光学吸收系数随压力的变化情况。结果表明:在高压作用下,Te原子和Zn原子的态密度分布都向低能量方向移动,分布范围增大,Te 5p和Zn3d电子轨道杂化变强。随着压力的增大,直接带隙逐渐增大,而间接带隙逐渐变小。当压力为10.7GPa时,能带结构从直接带隙转变为间接带隙结构。压力增大,有利于Te 5p与Zn3d电子间的跃迁,光吸收系数增大,产生更多的电子-空穴对,材料导电能力增强。     

不同构型(In,Al)GaN合金发光机理的第一性原理研究

基于第一性原理的密度泛函理论,研究了纤锌矿（In,Al）GaN合金的4种构型（均匀、短链、小团簇、团簇-链共存模型）的电子结构和发光微观机理。结果表明,在InGaN合金中,短In-N-链和小In-N团簇都局域电子在价带顶（VBM）态。当小团簇与短链共存时,前者局域电子的能力明显强于后者,是辐射复合发光中心。然而,在AlGaN合金中,电子在VBM态的局域受短Al-N链和小Al-N团簇的影响并不显著。合金微观结构的不同会引起电子局域的改变,从而影响材料的发光性能,并对带隙和弯曲系数有重要影响。     

Ga_(1–x)Cr_xSb(x=0.25,0.50,0.75)磁学和光学性质的第一性原理研究

随着高性能电子器件需求的日益增加,自旋电子学材料在材料研究和电子元件中具有重要地位,因为自旋电子学器件相比于传统半导体电子元件具有非易失性,低功耗和高集成度的优点.本文研究了Cr离子注入GaSb的电子性质、磁学和光学性质,采用基于密度泛函理论框架下的缀加投影平面波方法,利用广义梯度近似下电子交换关联泛函,考虑了Heyd-Scuseria-Ernzerhof(HSE06)杂化泛函计算进行电子能带带隙修正,首先对不同浓度Cr离子注入下的闪锌矿结构半导体GaSb形成的Ga_(1-x)Cr_xb(x=0.25,0.50,0.75)进行结构优化,计算了无磁、铁磁及反铁磁的基态能量,对比发现它们的基态均为铁磁态.对电子能带结构图分析发现,它们自旋向上的电子能带穿过费米面,而自旋向下的电子能带存在直接带隙,呈现铁磁半金属性质.同时在平衡晶格常数下具有整数倍玻尔磁矩,并在一定晶格变化范围内保持磁矩不变.同时发现它们在红外波段具有良好的吸收能力,这使得Ga_(1-x)Cr_xSb在自旋电子学器件和红外光电器件中拥有潜在的应用前景.     

ZnS中Te等电子中心的时间分辨光谱研究

用时间分辨光谱研究了很大的Te组分范围内的ZnS_1-xTe_x（x=00 05—085）合金的发光动力学特性，结果表明：不同形态的Te等电子中心具有不同的辐射复 合寿命，从几个ns到几十个ns的范围内变化，当x＝015左右时，寿命达到最大值（约 40ns）.其物理机理源于不同的Te等电子中心具有不同的局域化特性.当Te组分较小时，等 电子中心从Te₁逐渐演变到Te₂，Te₃或Te₄ 时，相应发光寿命增加，表现出不断增强 的激子发光局域化特性；而当Te组分较大时，Te原子团变得较大，其局域势与基体原子势的 相互作用增强，等电子中心的局域化特性减弱，而基体价带扩展态特征变得明显起来，相应 发光寿命逐渐减小.还研究了激子束缚能随Te组分的变化以及发光强度随温度的变化关系， 所得结果进一步支持了时间分辨光谱研究所得到的结论. 关键词： ZnS 等电子中心 时间分辨光谱 局域态     

Theoretical optoelectronic analysis of intermediate-band photovoltaic material based on ZnY1-xOx （Y = S,Se, Te） semiconductors by first-principles calculations

The structural, energetic, and electronic properties of lattice highly mismatched ZnY1-xOx （Y = S, Se, Te） ternary alloys with dilute O concentrations are calculated from first principles within the density functional theory. We demonstrate the formation of an isolated intermediate electronic band structure through diluted O-substitute in zinc-blende ZnY （Y = S, Se, Te） at octahedral sites in a semiconductor by the calculations of density of states （DOS）, leading to a significant absorption below the band gap of the parent semiconductor and an enhancement of the optical absorption in the whole energy range of the solar spectrum. It is found that the intermediate band states should be described as a result of the coupling between impurity O 2p states with the conduction band states. Moreover, the intermediate bands （IBs） in ZnTeO show high stabilization with the change of O concentration resulting from the largest electronegativity difference between O and Te compared with in the other ZnSO and ZnSeO.     

Oxygen incorporation in ZnTe thin films grown by plasma-assisted pulsed laser deposition

We studied oxygen incorporation into ZnTe thin films with nitrogen and oxygen plasma during a plasma-assisted pulsed laser deposition (PA-PLD). It was shown that ZnTe:O layer formed with oxygen plasma exhibits an enhancement of optical transparency in visible spectral region due to the formation of amorphous TeO_x. Especially, the ZnTe:NO deposited by PA-PLD under nitrogen and oxygen partial pressures with N₂:O₂ of 10:3 sccm showed p-type semiconducting characteristics and the formation of intermediate band at about 0.5–0.8 eV below the ZnTe band edge. These results for oxygen incorporation in ZnTe thin film such as the enhancement of optical transparency in visible spectral region and the intermediate band formation will be useful for optoelectronic devices or intermediate band solar cells.     

Single particle ground state of ZnTe:O

The ground state energy and wave function of an electron bound to isolectronic oxygen impurity in ZnTe are calculated. A highly localized state is found 0.17 eV from the bottom of the conduction band.     

Effect of oxygen implantation on ionoluminescence of porous silicon

We report on ionoluminescence investigations of porous Si prepared from the p⁺-type Si, which exhibited, after prolonged ambient air exposure, moderate photon emission with a maximum in the red–orange region. In an attempt to activate a shorter wavelength emission, the samples were implanted with 225 keV O⁺ ions at the dose of 1×10¹⁷ cm⁻². The strong blue band at 2.7 eV, well known in silica, has emerged in the ionoluminescence spectra following the oxygen implantation. The results of the comparative ionoluminescence experiments, performed on both porous Si and two forms of silica, show the important role of SiO₂ defect-related states in ion-induced optical emission from porous Si.     

Valence band contributions to photoluminescence excitation spectra of tightly bound holes in zincblende semiconductors

Photoluminescence excitation (PLE) spectra of deep acceptor states in ZnSe, for example the Cu-related luminescence band at ≈1.95 eV, contain a prominent excitation band at ≈3.25 eV. This band lies above the structure marking the lowest direct E_O band gap E_g by the spin-orbit splitting energy Δ of the valence bands at Γ. The higher energy feature is either absent or greatly de-emphasised in the PLE spectra of shallow acceptor states in ZnSe and of the oxygen iso-electronic trap in ZnTe, where the electron rather than the hole is tightly bound. However, a significant PLE component at E_g + Δ is observed for deep acceptor-like states in ZnTe, where Δ is ≈0.95 eV. Efficient PLE at E + Δ for luminescence from deep acceptor-like states is shown to be consistent with the extended wave-vector contributions to the bound state wave-functions of holes of binding energies ≈Δ.     

Optical properties of aluminum oxide after irradiation with cobalt ions

Optical absorption of leucoosapphire and polycrystalline corund (polycor) is studied after irradiation with cobalt ions and subsequent annealing in a vacuum. The structure of states localized in the forbidden band and induced by various imperfections has a higher stability to annealing as compared to the case of implantation of other types of ions into aluminum oxide. The fan-like behavior of the dose-dependent absorption spectra is a consequence of the defect-induced disordering of crystal lattices. It is determined that intrinsic radiation-induced defects, substitutional defects, complexes containing them, and Co nanoparticles have an influence on the parameters of the focal point of the absorption spectra. The parameters of the interband and exponential absorption demonstrate the formation of a new multidefect material with a band gap width ranging from 5.3 to 5.5 eV and an absorption edge at 2.0–5.2 eV caused by the localized states of defect clusters.     

Mg~(2+)掺杂锰酸锂的第一性原理研究

利用基于密度泛函理论的第一性原理平面波超软赝势法对Mg~(2+)掺杂锰酸锂的晶格常数与能带结构、态密度、键布居进行计算和分析,计算结果表明:掺杂Mg~(2+)后将会促使Mn、 O原子的电荷重新分布且其相互作用加强,能带带隙减小,费米能级附近的带数增加,费米能由-1.29 eV增加到-1.02 eV, Mn、 O、 Mg在总态密度中贡献比较大,锂离子贡献比较小且峰型尖锐局域化严重,提高了Li~+的扩散效率, Mn—O键变短,共价性增强,形成的共价键较稳定,其相互作用形成的骨架较稳定不易坍塌.从而提高了材料的循环充放电性能和电池使用寿命.     

Interaction of localized electronic states with the conduction band: band anticrossing in II-VI semiconductor ternaries

We report a strongly nonlinear pressure dependence of the band gaps and large downward shifts of the conduction band edges as functions of composition in ZnS xTe (1-x) and ZnSe (y)Te (1-y) alloys. The dependencies are explained by an interaction between localized A1 symmetry states of S or Se atoms and the extended states of the ZnTe matrix. These results, combined with previous studies of III-N-V materials define a new, broad class of semiconductor alloys in which the introduction of highly electronegative atoms leads to dramatic modifications of the conduction band structure. The modifications are well described by the recently introduced band anticrossing model.     

Electrical conductivity and band structure of thin polycrystalline EuS films

A study of the electrical resistance of thin polycrystalline EuS films (0.4–0.8 μm thick) in the temperature range 120–480 K has provided the basis for a model of the band structure of this substance. It has been shown that the main impurity levels in thin polycrystalline EuS films are those related with localized states near the conduction band bottom, as well as the E _i donor levels of Eu ions outside regular lattice sites. The “tail” of the localized states extends in energy up to at least ?0.45 eV.     

Surface states due to deposited alkaline earth cations on ZnO

Surface states due to Be, Mg, Ca, Sr, and Ba ions deposited on ZnO as salts with varying anions have been examined, to make available a selection of nonvolatile surface states for later study, and to provide a relatively simple group of substitutional surface states that could be used to compare theories with experiment. The results indicate that Be⁺⁺ and Ba⁺⁺ additions lead to shallow acceptor levels, near or above the ZnO conduction band, while deeper acceptor levels (as low as 0.9 eV below the conduction band) are associated with Mg⁺⁺, Ca⁺⁺, and Sr⁺⁺ additions. The energy of the resulting surface state depends somewhat on whether the alkaline earth species is added as the hydroxide or the fluoride. There is evidence of a high density donor level at 1.1 eV below the conduction band perhaps associated with surface lattice oxygen or with OH^? groups. Arguments arepresented suggesting that the surface state is associated with the alkaline earth ions at lattice sites at the ZnO/additive interface, and some of the factors are discussed that must be considered in a theoretical model.