二维缺陷GaAs电子结构和光学性质第一性原理研究

采用基于密度泛函理论的第一性原理方法计算了存在Ga空位缺陷和掺杂B原子的二维GaAs的能带结构、态密度和光学性质.计算结果表明空位缺陷二维GaAs显示出金属特性,B原子的引入使体系变为间接带隙半导体,禁带宽度为0.35 eV.态密度计算发现体系低能带主要由Ga的s态、p态、d态和As的s态、p态构成;高能带主要由Ga和As的s态、p态构成.掺杂B原子与存在空位缺陷的二维GaAs相比,静态介电常数相对较低,变为8.42,且易于吸收紫外光,在3.90～8.63 eV能量范围具有金属反射特性,反射率达到52%.     

Effect of Ga and As vacancies on electronic properties of Ga0.9375Al0.0625As

Electronic properties of Ga_0.9375Al_0.0625As with Ga and As monovacancies are investigated with the density functional theory. A perfect GaAlAs, which specifically produces a radiation wavelength of ～825.6 nm, has been determined in terms of size and number of atoms of substances. We have introduced eight types of vacancies depending on the distance from the Al atom to the vacancy to obtain the changes in charges, band structures, density of states, and optical conductivity. We found that the Fermi level enters into the valence band due to the formations of the Ga or As vacancies so that the vacant materials may show the characteristics of the p-type semiconductor. Interestingly, Ga-vacancy systems make direct band gaps, which are still good for the use in a semiconductor laser. But, As-vacancy systems, where the indirect gaps appear, are not feasible for the same application. It has been found that the latter phenomenon is induced by a newly formed density of state, which comes from the overlapping of hybridised 4s and 4p orbitals of Ga atoms around As vacancy.     

Electronic Structures of Wurtzite GaN with Ga and N Vacancies

The electronic band structures of wurtzite GaN with Ga and N vacancy defects are investigated by means of the first-principles total energy calculations in the neutral charge state. Our results show that the band structures can be significantly modified by the Ga and N vacancies in the GaN samples. Generally, the width of the valence band is reduced and the band gap is enlarged. The defect-induced bands can be introduced in the band gap of GMV due to the Ga and N vacancies. Moreover, the GaN with high density of N vacancies becomes an indirect gap semiconductor. Three defect bands due to Ga vacancy defects are created within the band gap and near the top of the valence band. In contrast, the N vacancies introduce four defect bands within the band gap. One is in the vicinity of the top of the valence band, and the others are near the bottom of the conduction band. The physical origin of the defect bands and modification of the band structures due to the Ga and N vacancies are analysed in depth.     

GGA+U方法研究C-Al掺杂GaN的电子结构和光学性质

本文用密度泛函理论的第一性原理,研究了C单掺、Al单掺、C-Al共掺GaN体系的电子结构及光学性质.通过分析发现,与本征GaN相比,掺杂后体系都发生了晶格畸变,其中C-Al共掺GaN体系,较容易形成且禁带宽度明显减小,形成了P型半导体,显著降低了电子跃迁所需要的能量;另外,该共掺体系的静介电常数最大,极化能力最强,介电虚部的主峰向低能区域偏移,并且吸收光谱在可见光范围内产生了红移现象,这都体现了C-Al共掺可以拓展GaN体系对可见光的响应范围.因此,C-Al共掺将有望提高GaN体系的光催化性能.     

空位浓度对纤锌矿BN电子结构和光学性质影响的第一性原理研究

本文采用了第一性原理研究了空位缺陷纤锌矿BN的电子结构和光学性质.通过对能带结构、态密度分析发现：缺陷体系由于B、N的缺失,费米能级附近出现杂质能级.相较于本征体系,随着空位浓度增加,杂质能级变多,跃迁能量减小. N空位缺陷的纤锌矿BN态密度总体向低能区移动,且能级相较于B空位缺陷的纤锌矿BN明显增多.从复介电函数和光学吸收谱分析中发现,随着空位浓度的增加,缺陷体系纤锌矿BN在可见光区域的吸收逐渐增强.尤其是B₂₂N₂₄在可见光区域出现的吸收效果更好.     

Electronic structure and optical properties of Al and Mg co-doped GaN

The electronic structure and optical properties of Al and Mg co-doped GaN are calculated from first principles using density function theory with the plane-wave ultrasoft pseudopotential method.The results show that the optimal form of p-type GaN is obtained with an appropriate Al:Mg co-doping ratio rather than with only Mg doping.Al doping weakens the interaction between Ga and N,resulting in the Ga 4s states moving to a high energy region and the system band gap widening.The optical properties of the co-doped system are calculated and compared with those of undoped GaN.The dielectric function of the co-doped system is anisotropic in the low energy region.The static refractive index and reflectivity increase,and absorption coefficient decreases.This provides the theoretical foundation for the design and application of Al–Mg co-doped GaN photoelectric materials.     

Mn掺杂GaN稀磁半导体的电磁特性研究

采用基于密度泛函理论的第一性原理平面波超软赝势法计算了不同浓度Mn掺杂GaN(Ga1-xMnxN,x=0.0625和0.1250)的晶格常数、能带结构和态密度,分析比较了掺杂前后GaN的电子结构和磁性.结果表明:Mn掺入后体系仍为直接带隙半导体,带隙宽度随Mn含量的增加逐步增大.Mn掺杂GaN均使得N2p与Mn3d轨道杂化,产生自旋极化杂质带,自旋向上的能带占据费米面,掺杂后的Ga1-xMnxN表现为半金属铁磁性,适合自旋注入;随着Mn掺杂浓度的增加,体系的半金属性有所增强.     

Mn掺杂GaN稀磁半导体的电磁特性研究

采用基于密度泛函理论的第一性原理平面波超软赝势法计算了不同浓度Mn掺杂GaN（Ga1-xMnxN, x=0.0625和0.1250）的晶格常数、能带结构和态密度,分析比较了掺杂前后GaN的电子结构和磁性。结果表明：Mn掺入后体系仍为直接带隙半导体,带隙宽度随Mn含量的增加逐步增大。Mn掺杂GaN均使得N 2p与Mn 3d轨道杂化,产生自旋极化杂质带,自旋向上的能带占据费米面,掺杂后的Ga1-xMnxN表现为半金属铁磁性,适合自旋注入;随着Mn掺杂浓度的增加,体系的半金属性有所增强。     

六方氮化硼单层中一种(CN)3VB缺陷的第一性原理计算

二维六方氮化硼(hBN)的点缺陷最近被发现可以实现室温下的单光子发射,而成为近年的研究热点.尽管其具有重要的基础和应用研究意义,hBN中发光缺陷的原子结构起源仍然存在争议.本文采用基于密度泛函理论的第一性原理计算,研究hBN单层中一种B空位附近3个N原子被C替代的缺陷(CN)3VB.在hBN的B空位处,3个N原子各自带一个在平面内的悬挂键及相应的未配对电子,而通过C替换可以消除未配对的电子.系统研究了(CN)3VB缺陷的几何结构、电子结构以及光学性质,结果表明,缺陷可以由一个对称的亚稳态经过原子结构弛豫变成1个非对称的、3个C原子连在一起的基态结构.缺陷的形成在hBN中引入了一些由缺陷悬挂σ键及重构的π键贡献的局域缺陷态.这些缺陷态可以导致能量阈值在2.58 eV附近的可见光内部跃迁.本文的工作有助于进一步理解hBN中点缺陷的构成及光学性质,为实验上探讨发光点缺陷的原子结构起源及其性质提供理论依据.     

硼氮掺杂对立方PbTiO3电子结构和光学性质影响的第一性原理研究

钛酸铅(PTO)因具有优异的铁电、压电特性及光学性质而备受关注.但B、N掺杂对顺电相PTO电子结构和光学性质的影响还不明确,因此,利用第一性原理对立方PTO开展准确的性质预测尤为必要.本文采用广义梯度近似的PBE泛函(GGA-PBE)和杂化泛函(HSE06)研究了B、N替位掺杂(B_O、N_O)和O空位(V_O)对PTO的基态性质、电子结构和光学性质的影响.研究表明：贫氧态的PTO比富氧态更容易形成杂质缺陷,且N_O缺陷最难形成.当B_O、N_O缺陷存在时,PTO的价带顶和导带底向低能量方向移动,在两者之间出现杂质能级,使其导电性能提高且含B_O的PTO为间接带隙半导体,而含N_O的PTO为直接带隙半导体. N_O体系在波长大约为230 nm处有最大吸收峰,该峰主要源于O 2p和Ti 3d之间的电子跃迁,且N_O体系对可见光的吸收能力最强,有望提高PTO的光催化能力.     

石墨烯/BiOI纳米复合物电子结构和光学性质的第一性原理模拟计算

光催化材料在解决能源短缺和环境污染等问题方面具有广泛的应用前景,本文通过构建BiOI纳米薄膜并将其与石墨烯复合起来,得到具有较高的比表面积和良好的光催化活性的纳米复合物光催化材料.采用基于密度泛函理论的第一性原理方法分别计算了单层和双层BiOI纳米片及其与石墨烯复合结构的电子结构和光学性质,并考虑了BiOI中的Bi,O,I三种空位缺陷对电子结构和光学特性的影响.计算结果表明,由于BiOI和石墨烯之间的相互作用,在石墨烯和BiOI界面处自发发生电荷转移,形成电子-空穴对,且石墨烯衬底可有效提高BiOI对可见光的光吸收,提高其光催化活性.对空位缺陷的计算表明,Bi空位缺陷可促进石墨烯和BiOI之间的电荷转移,形成更多的层间电子-空穴对;相反,O和I空位缺陷则抑制层间电荷转移,减少电子-空穴对的生成.     

First-principles study on anatase TiO2（101） surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide （NO） adsorption on the anatase TiO2 （101） surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV （N end adsorption）, 2.6770 eV （O end adsorption）, and 4.1437 eV （horizontal adsorption）. The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 （101） surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 （101） surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.     

空位缺陷对β-AgVO_3电子结构和光吸收性能的影响

基于密度泛函的第一性原理研究了Ag空位、O空位和Ag-O双空位对β-AgVO_3的电子结构及光学性质的影响.采用广义梯度近似平面波超软赝势GGA+U方法,对不同缺陷体系的形成能、能带结构、电子态密度、差分电荷密度和吸收光谱进行了计算和分析.通过比较不同Ag空位和O空位的形成能,确定了β-AgVO_3中主要形成Ag3空位和O1空位,并且Ag空位较O空位更容易形成.Ag3空位和O1空位的存在都使得β-AgVO_3带隙有一定程度的减小;Ag3空位使β-AgVO_3呈现p-型半导体性质,而O1空位和Ag3-O1双空位使β-AgVO_3呈现n-型半导体性质.Ag3和O1空位对晶体在可见光范围内的光吸收影响较小.     

闪锌矿结构AlSb空位缺陷性质的第一性原理研究

采用基于密度泛函理论(DFT)第一性原理的平面波超软赝势方法，计算含有锑空位和铝空位的电子结构，发现空位引起周围原子弛豫，晶体结构发生畸变。在此基础上研究了空位缺陷对闪锌矿型AlSb体系电子结构的影响，结果表明，铝空位缺陷使锑化铝费米能级降低，带隙变窄；而锑空位缺陷则使锑化铝费米能级升高，带隙变窄，同时，锑化铝的半导体类型由p型变为n型。对光学性质的研究发现，由于空位的引入使其邻近原子电子结构发生变化，使得空位缺陷系统光学性质的变化主要集中在低能量区域。     

闪锌矿结构AlSb空位缺陷性质的第一性原理研究

采用基于密度泛函理论(DFT)第一性原理的平面波超软赝势方法,计算含有锑空位和铝空位的AlSb电子结构,发现空位引起周围原子弛豫,晶体结构发生畸变.在此基础上研究了空位缺陷对闪锌矿型AlSb体系电子结构的影响,结果表明,铝空位缺陷使锑化铝费米能级降低,带隙变窄;而锑空位缺陷则使锑化铝费米能级升高,带隙变窄,同时,锑化铝的半导体类型由p型变为n型.对光学性质的研究发现,由于空位的引入使其邻近原子电子结构发生变化,使得空位缺陷系统光学性质的变化主要集中在低能量区域.     

应变对两层半氢化氮化镓薄膜电磁学性质的调控机理研究

采用基于密度泛函理论的第一性原理模拟计算,研究了在应变作用下两层半氢化氮化镓纳米薄膜的电学和磁学性质.没有表面修饰的两层氮化镓纳米薄膜的原子结构为类石墨结构,并具有间接能隙.然而,当两层氮化镓纳米薄膜的一侧表面镓原子被氢化时,该纳米薄膜却依然保持纤锌矿结构,并且展示出铁磁性半导体特性.在应变作用下,两层半氢化氮化镓纳米薄膜的能隙可进行有效调控,并且它将会由半导体性质可转变为半金属性质或金属性质.这主要是由于应变对表面氮原子的键间交互影响和p-p轨道直接交互影响之间协调作用的结果.该研究成果为实现低维半导体纳米材料的多样化提供了有效的调控手段,为其应用于新型电子纳米器件和自旋电子器件提供重要的理论指导.     

Ga vacancy induced ferromagnetism enhancement and electronic structures of RE-doped GaN

Because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors (DMSs) doped by rare-earth (RE) elements have attracted much attention since the high Curie temperature was obtained in RE-doped GaN DMSs and a colossal magnetic moment was observed in the Gd-doped GaN thin film. We have systemically studied the GaN DMSs doped by RE elements (La, Ce–Yb) using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. We have studied the electronic structures of DMSs, especially for the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. We found that, for materials containing f electrons, electronic correlation was usually strong and the spin–orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm are stabilized at antiferromagnetic phase, while GaN doped by other RE elements show strong ferromagnetism which is suitable materials for spintronic devices. Moreover, we have identified that the observed large enhancement of magnetic moment in GaN is mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the RE doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of RE-doped semiconductors in the third generation high efficiency photovoltaic devices.     

含空位二维六角氮化硼电子和磁性质的密度泛函研究

基于密度泛函理论的第一性原理计算, 研究了含B原子空位(V_B), N原子空位(V_N), 以及含B–N键空位 (V_B+N)缺陷的二维氮化硼(h-BN)的电子和磁性质. 在微观结构上, V_B体系表现为在空位附近的N原子重构成等腰三角形, V_N体系靠近空穴的B 原子形成等边三角形, V_B+N体系靠近空穴处的B和N原子在h-BN平面上重构为梯形. 三种空位缺陷都使h-BN的带隙类型从直接带隙转变为间接带隙. V_B体系的总磁矩为1.0 μ_B, 磁矩全部由N原子贡献. 其中空穴周围的三个N原子磁矩方向不完全一致, 存在着铁磁性和反铁磁性两种耦合方式. 对于V_N 体系, 整个晶胞内的总磁矩也为1.0 μ_B, 磁矩在空穴周围区域呈现一定的分布. 关键词： 二维h-BN 空位 电子结构 磁性     

Cd、Sr掺杂Mg2Ge电子结构和光学性质的第一性原理研究

此文用基于密度泛函理论(DFT)的第一性原理计算方法,分别研究了本征、掺Cd、掺Sr的Mg₂Ge的能带结构、电子态密度和光学性质.研究结果表明,本征Mg₂Ge是一种间接带隙半导体,带隙值为0.228eV.Sr的掺入使其变成带隙为0.591 eV的直接带隙半导体,Cd掺杂Mg₂Ge后表现出半金属性质.掺杂后的主要吸收峰减小,吸收谱范围增加.在可见光能量范围内,掺杂的Mg₂Ge有更低的反射率,对可见光的利用率增强.此外,掺杂还提高了高能区的光电导率.     

Vacancy defects as compensating centers in Mg-doped GaN

We apply positron annihilation spectroscopy to identify V(N)-Mg(Ga) complexes as native defects in Mg-doped GaN. These defects dissociate in postgrowth annealings at 500-800 degrees C. We conclude that V(N)-Mg(Ga) complexes contribute to the electrical compensation of Mg as well as the activation of p-type conductivity in the annealing. The observation of V(N)-Mg(Ga) complexes confirms that vacancy defects in either the N or Ga sublattice are abundant in GaN at any position of the Fermi level during growth, as predicted previously by theoretical calculations.