Be1-xMgxO合金的能带特性与相结构稳定性研究

采用基于密度泛函理论的平面波赝势方法,对纤锌矿和岩盐矿结构Be_1-xMg_xO合金的晶格常数、能带特性和形成能进行计算,分析了不同Mg组分下不同结构的Be_1-xMg_xO合金晶格常数和能带差异.结果表明:随着Mg组分的增大,纤锌矿和岩盐矿Be_1-xMg_xO合金的晶格常数都线性增加,但它们的能隙都逐渐减小.对于相同Mg组分的Be_1-xMg_xO合金,岩盐矿结构的能隙要大于纤锌矿结构.当Mg组分为0.89时,Be_1-xMg_xO合金由纤锌矿相转变为岩盐矿相.为了使理论值与实验值相一致,对Be_1-xMg_xO合金的能隙计算值进行修正,得到纤锌矿和岩盐矿Be_1-xMg_xO合金的能隙弯曲系数b值分别为3.451 eV和4.96 eV.对纤锌矿BeO-MgO-ZnO三元合金的能隙和弯曲系数与晶格常数关系做了分析.     

Nb掺杂影响NiTi金属间化合物电子结构的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了Nb元素掺杂对B2构型NiTi金属间化合物电子结构的影响.点缺陷生成能的计算结果表明,Nb原子掺杂后,NiTi中产生Ni原子和Ti原子空位和反位点缺陷所需要的能量均明显升高;态密度计算结果表明,Nb原子掺杂后与临近原子发生了明显的s-s, p-p和d-d电子相互作用,增加了与临近原子之间的电荷密度,有利于Nb与合金原子的成键.这些由Nb掺杂所导致的NiTi电子结构和键合特征的变化均有利于促进Nb与合金原子的相互作用,在一定程 关键词： NiTi金属间化合物 点缺陷 电子结构 第一性原理计算     

Cd:O共掺杂AlN的电子结构和p型特性研究

为研究Cd：O共掺杂纤锌矿AlN的p型特性,进而揭示导致纤锌矿AlN空穴浓度增加的机理,对Cd：O共掺杂AlN进行了基于密度泛函理论的第一性原理研究.通过计算Cd_n-O（n=1,2,3,4）复合体掺杂AlN的结合能,发现Cd：O在AlN中可以稳定存在,共掺杂提高了Cd在AlN中的固溶度.分析Cd和Cd₂-O掺杂AlN体系的激活能,发现Cd₂-O的激活能比Cd减小0.21 eV,表明Cd₂-O的空穴浓度比单掺Cd大约提高 关键词： Cd：O共掺杂 纤锌矿AlN 电子结构 p型掺杂特性     

纤锌矿结构ZnO中定位Ga-N共掺杂对p型掺杂效率的影响

采用第一性原理和密度泛函理论的方法,计算未掺杂、N单掺杂和Ga-N共掺杂纤锌矿结构ZnO的总能、电荷密度和能带结构.总能计算表明,Ga原子的共掺杂使总能极大地降低,从而显著提高杂质N原子在ZnO中的稳定性.电荷密度分布显示,总能的降低主要是Ga-N共掺杂后Ga原子的3d态和N原子的2p态电子之间的强杂化相互作用所致.特别是在Ga原子的负电荷和N原子的正电荷沿c轴排成一线的共掺杂构型中,较大的局域极化场的变化引起价带顶向禁带中的大分裂,降低了N受主的激活能,将空穴的浓度提高了三个量级,有效地提高p型掺杂效率.     

Mg，Cu 掺杂CdS电子结构的第一性原理研究

采用基于密度泛函理论（DFT）的第一性原理的平面波超软赝势方法,对闪锌矿结构CdS晶体及CdS:M（M=Mg, Cu）的几何结构、能带结构、电子态密度、集聚数和电荷密度分布进行了研究.对掺杂后体系的几何结构进行了优化计算,发现Mg和Cu原子掺入CdS后晶格常量均减少,晶格发生畸变.在此基础上研究了掺杂对体系电子结构的影响.结果表明,Mg,Cu掺入CdS都能提供较多空穴态,形成p型电导,并且Cu较Mg是更好的p型掺杂剂. 关键词： 密度泛函理论 电子结构 p型掺杂     

Cd_xZn_(1-x)O合金热力学性质的第一性原理研究

ZnO的能带工程是当前ZnO研究的热点之一通过等价阳离子如Cd,Be,Mg等部分取代Zn形成CdZnO,BeZnO,MgZnO等合金来调控ZnO带隙的研究己广泛开展.其中,Cd的掺杂可以减小ZnO的禁带宽度,使CdZnO合金在紫外一可见光波段光电器件中具有潜在的应用价值.本文利用第一性原理计算结合集团展开法,通过研究纤锌矿(WZ)和岩盐矿(RS)型Cd_xZn_(1-x)O合金不同Cd掺杂含量下各种构型的形成能,发现了纤锌矿结构的两种亚稳相Cd_(1/3)Zn_(2/3)O,Cd_(2/3)Zn_(1/3)O;对其晶格常数·键长·键角和电子结构的分析表明,随着Cd掺杂量的增大,晶格常数a,c均逐渐增大,而c/a值逐渐减小,O—Zn(Cd)—O键角及合金禁带宽度均逐渐减小.通过对Cd_xZn_(1-x)O合金的有效集团交互系数的分析得出,两个原子组成的集团中其有效集团交互系数最大,表明两原子集团对用集团展开法计算的形成能贡献最大.通过比较第一性原理计算的形成能和集团展开法拟合计算得到的形成能,发现两者相差很小,表明采用集团展开法拟合计算Cd_xZn_(1-x)O合金的形成能准确、可靠,通过对大量Cd_xZn_(1-x)O合金的形成能分析发现,大部分Cd_xZn_(1-x)O的形成能比同组分的ZnO与CdO混合相的能量高,表明ZnO和CdO互溶时会形成固溶度间隙,低温下难以实现全组分固溶.在此基础上,我们计算了WZ-和RS-Cd_xZn_(1-x)O随机合金的形成能并得到了相图.对于纤锌矿结构,其临界温度为1000 K;对于岩盐矿结构,其临界温度为2250 K.更高的临界温度表明Cd_xZn_(1-x)O难以形成岩盐矿结构的合金.进一步计算获得WZ-和RS-Cd_xZn_(1-x)O的两相相图,发现Cd较易固溶于WZ-ZnO中,而Zn较难固溶于RS-CdO中.     

Mn掺杂ZnO光学特性的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法计算了纤锌矿ZnO及不同量Mn 掺杂ZnO 晶体的电子结构,分析了掺杂对ZnO 晶体的能带结构、电子态密度、差分电荷分布的影响. 计算结果表明,随着Mn 掺杂含量的增加,ZnO 禁带宽度相应增加并且对紫外吸收区的光吸收能力也随之增强. 关键词： 密度泛函理论(DFT) 第一性原理 超软赝势 Mn掺杂ZnO     

纤锌矿CdxZn1-xO电子结构的第一性原理研究

采用第一性原理的平面波超软赝势方法,计算了纤锌矿ZnO及不同量Cd掺杂ZnO的电子结构.计算结果表明,Cd的掺杂导致ZnO晶体的禁带宽度变窄.主要原因在于Cd的掺入导致Zn4s轨道中能级越来越低的电子参与作用,使得决定导带底的反键Zn 4s态能级逐渐降低,同时由pd反键轨道控制的价带顶能级逐渐升高. 关键词： 密度泛函理论 超软赝势方法 Cd掺杂ZnO     

Be和Ca掺杂纤锌矿ZnO的晶格常数与能带特性研究

利用密度泛函理论平面波的赝势方法,对Be、Ca掺杂纤锌矿ZnO的BexZn1-xO,CayZn1-xO三元合金和BexZn1-xO,CayZn1-xO四元合金的晶格常数、能带特性和形成能进行计算,结果表明：BexZn1--xO晶格常数随Be掺杂量的增大线性减小,但CayZn1-yO晶格常数随ca掺杂量的增大而增大．BexZn1-xO和CayZn1-yO能带的价带顶都由O2p态电子占据,导带底由Zn4s态电子占据,其能隙随Be或Ca掺杂量的增大而变宽．由Be和Ca共掺ZnO得到的Be0．125Ca0．125Zn0．75O四元合金,其晶格常数与ZnO相匹配,能隙比ZnO大,稳定性优于Be0．25Ca0．125Zn0.625O和Be0．5Zn0．50合金,Be0．125Ca0．125Zn0.75O／ZnO异质结构适合制作高质量ZnO基器件．     

TiN多型体高压相变的第一性原理计算

基于密度泛函理论框架下的赝势平面波方法,计算了B1(氯化钠结构)、B2(氯化铯结构)、B3(闪锌矿结构)、B_k(六方氮化硼结构)、B_h(碳化钨结构)和B8₁(砷化镍结构)6种TiN多型体的晶体结构、体积弹性模量和相对稳定性.计算指出,不存在B4(纤锌矿)结构的TiN.通过不同外压下的晶格弛豫得到每种结构的焓,发现外压 关键词： 氮化钛 赝势 高压相变 密度泛函理论     

Study on the doping stability and electronic structure of wurtzite Zn1−xCdxO alloys by first-principle calculations

An ab initio calculation based on density functional theory is applied to study the doping stability and electronic structure of wurtzite Zn_1−xCd_xO alloys. It is found that the different alloy configurations of Zn_1−xCd_xO with a given Cd content are possible thermodynamically, but having different band gaps. With increasing Cd content, the formation enthalpy of Zn_1−xCd_xO alloy increases sharply. The Cd-content dependence of the band-gap values can be fitted with a second-order polynomial. The reduction of band gap can be attributed to the contributions of the hybridization of Zn-4s and Cd-5s, the enhancement of p-d repulsion, and the tensile strain due to Cd-doping.     

GaxAlyIn1-x-yN电子结构的第一原理虚晶近似计算

对Ga_xAl_yIn_1-x-yN四元合金材料进行了第一原理的虚晶近似计算.分别计算了在两种不同晶体结构，即纤锌矿结构和闪锌矿结构下的合金电子结构，特别是能隙随混晶比(x,y)的变化.得出了纤锌矿结构下能隙E_g和组分(x,y)的关系式. 关键词：     

Structural,electronic and optical properties of CdxZn1 − xS alloys from first-principles calculations

Structural, electronic and optical properties as well as structural phase transitions of ternary alloy Cd_xZn_1 − xS have been investigated using the first-principles calculations based on the density functional theory. We found that the crystal structure of Cd_xZn_1 − xS alloys transforms from wurtzite to zinc blende as Cd content of x=0.83$x=0.83$. Effect of Cd content on electronic structures of Cd_xZn_1 − xS alloys has been studied. The bandgaps of Cd_xZn_1 − xS alloys with wurtzite and zinc blende structures decrease with the increase of Cd content. Furthermore, dielectric constant and absorption coefficient also have been discussed in detail.     

Structural and electronic properties of wurtzite,zincblende and rocksalt Al1 − xInxN ternary alloys at ambient and high pressure

ABSTRACT

Although AlInN is originally a wurtzite structure, zincblende and rocksalt are other potential phases. It will be interesting to have a comparative study of the physical properties of this compound in various phases. A DFT-based study of wurtzite, zincblende and rocksalt phases of AlInN alloys is carried out. Structural (lattice parameter, bulk modulus) and electronic properties (energy band gap, and electron effective mass) of the Al_{1??? x}In_xN alloys are investigated, at ambient pressure, throughout the whole range of indium contents for all considered phases. High pressure effects on the studied parameters are also examined, with the phase transition pressures computed for different values of In concentrations, and compared with available data. Structural density functional calculations are performed with Perdew–Burke–Ernzerhof gradient-corrected functional for solids (PBEsol), while electronic structure is computed with the modified Becke–Johnson (TB-mBJ) potential exchange to ensure a better accuracy of calculated the band gaps. Alloy randomness is taken into account using a special quasi-random structure.     

纤锌矿BeO掺Cd的电子结构与能带特性研究

采用基于密度泛函理论平面波赝势方法, 对纤锌矿BeO掺Cd的Be_1-xCd_xO合金进行电子结构与能带特性研究. 结果表明: Be_1-xCd_xO的价带顶始终由O 2p电子态决定, 而导带底由Be 2s和Cd 5s的电子态决定.随着Be_1-xCd_xO合金的Cd掺杂量增加, Cd 4d与O 2p的排斥效应逐渐加强, 同时Be_1-xCd_xO的带隙逐渐变小, 出现"直接-间接-直接"的带隙转变. 为了使理论值与实验值相一致, 对Be_1-xCd_xO带隙进行修正, 并分析了纤锌矿BeO-ZnO-CdO三元合金的带隙和弯曲系数与晶格常数的关系.     

Effect of post annealing temperature on structural and optical properties of ZnCdO thin films deposited by sol–gel method

Ternary ZnCdO thin films oriented along c-axis have been successfully deposited on p-Si (1 0 0) substrates using sol–gel spin coating route. To optimize most suitable annealing temperature for the Zn_1−xCd_xO thin films; these films with selected cadmium content x = 0.10 were treated at annealing temperatures from 300 °C up to 800 °C in oxygen ambient after deposition. The structural and optical properties of deposited thin films have been characterized by X-ray diffraction, energy dispersive spectroscopy, atomic force microscopy, UV–Vis spectroscopy, and photoluminescence spectra. The results show that the obtained films possess high crystallinity with wurtzite structure. The crystallite size, lattice parameters, lattice strain and stress in the deposited films are determined from X-ray diffraction analysis. The band gap energy increased as a function of annealing temperatures as observed from optical reflectance spectra of samples. The presence of Cd in the deposited films is confirmed by energy dispersive spectrum and it is observed that Cd re-evaporate from the lattice with annealing. The photoluminescence measurements as performed at room temperature did not exhibit any luminescence related to oxygen vacancies defects for lower annealing temperatures, as normally displayed by ZnO films. The green yellow luminescence associated to these defects was observed at higher annealing temperatures (≥700 °C).     

Theoretical prediction of structural, electronic and optical properties of quaternary alloy Zn1-xBexSySe1-y

Within density functional theory based on the full potential-linearized augmented plane wave method, we carry out the first-principles calculation of the structural, electronic, and optical properties of the zinc blende quaternary alloy Zn_1-xBe_xS_ySe_1-y. The Perdew-Burke-Ernzerhof generalized gradient approximation based on the optimization of total energy and the Engel-Vosko generalized gradient approximation based on the optimization of the corresponding potential are used. Our investigation on the effect of the composition on lattice constants, bulk modulus, band gap, optical dielectric constant, and refractive index shows a non-linear dependence. The energy gap E_g(x, y) has been determined over the entire compositions x and y. In addition, the energy band gap of the technologically important quaternary alloy Zn_1-xBe_xS_ySe_1-y in conditions of being lattice matched to ZnS substrate has been investigated. It is noteworthy that the present work is the first theoretical study of the quaternary alloy of interest.     

Microscopic indium distribution and electron localization in zinc blende InGaN alloys and InGaN/GaN strained quantum wells

In order to give an atomic level understanding of the light emission mechanism and seek In distribution patterns closely related to the elusive electron localization centers, we optimize the crystal structure of zinc blende In _x Ga_1−x N (0≤x≤1) alloys with different In distributions and investigate their electronic structures using first-principles calculations. Our results show that In _x Ga_1−x N forms a random alloy, in which several-atom In–N clusters and In–N chains can exist stably with a high concentration due to their small formation energy. These In–N clusters and chains form more easily in zinc blende structure than in wurtzite structure. The band gap of zinc blende In _x Ga_1−x N alloys insensitively depends on the In distribution. Moreover, we find that both small In–N clusters and straight In–N chains with three or more In atoms, acting as radiative recombination centers, highly localize the electrons of the valence band maximum state and dominate the light emission of Ga-rich In _x Ga_1−x N alloys. The strains of In _x Ga_1−x N layers can enhance the electron localization in In _x Ga_1−x N/GaN strained quantum wells. Our results are in good agreement with experiments and other calculations.     

Cd掺杂纤锌矿ZnO电子结构的第一性原理研究

采用密度泛函理论结合投影缀加波方法，对掺杂Cd导致ZnO禁带宽度下降的机理进行了研究. 通过对掺杂前后电子能带结构，态密度以及分态密度的计算和比较，发现Cd_xZn_1-xO价带顶端(VBM)始终由O-2p占据；而导带顶端(CBM)则由Cd-5s与Zn-4s杂化轨道控制. 随着掺杂浓度的增加，决定带隙宽度的CBM的位置下降，同时VBM的位置上升，从而导致了带隙的变窄，出现了红移现象. 此外，Cd掺杂会使晶胞发生膨胀，这种张应变也是导致Cd     

Cd掺杂纤锌矿ZnO电子结构的第一性原理研究

采用密度泛函理论结合投影缀加波方法,对掺杂Cd导致ZnO禁带宽度下降的机理进行了研究. 通过对掺杂前后电子能带结构,态密度以及分态密度的计算和比较,发现Cd_xZn_1-xO价带顶端(VBM)始终由O-2p占据;而导带顶端(CBM)则由Cd-5s与Zn-4s杂化轨道控制. 随着掺杂浓度的增加,决定带隙宽度的CBM的位置下降,同时VBM的位置上升,从而导致了带隙的变窄,出现了红移现象. 此外,Cd掺杂会使晶胞发生膨胀,这种张应变也是导致Cd 关键词： 密度泛函理论 电子结构 Cd掺杂ZnO