宽带隙半导体CdAl_2S_4电子结构、弹性和光学性质的研究

采用基于密度泛函理论(DFT)的第一性原理计算方法,对宽带隙半导体Cd Al_2S_4的晶格结构、电学、弹性和光学性能进行了系统的研究.研究结果表明:Cd Al2S4为直接带隙的宽带隙半导体材料;是弹性稳定的具有各向异性的延展性材料;该晶体的光学性质在中能区(3.5~12.5 e V)具有较强的各向异性,其强反射峰处于紫外能量区域,因此其可用作紫外光探测或屏蔽材料.     

电场调控双层石墨烯纳米带的电子结构和光学性质

利用基于密度泛函理论的第一性原理方法,研究了外加电场作用下双层AA堆垛的Armchair边缘石墨烯纳米带(BAGNRs)的电子结构和光学性质. BAGNRs具有半导体特性,其带隙随带宽(宽度为4～12个碳原子)的增加而振荡性减小.当施加电场后,BAGNRs的带隙随着电场强度的增加而逐渐减小,带隙越大对电场值的变化越敏感.当电场值为0.5 V/?时,所有BAGNRs的带隙都为零. BAGNRs具有各向异性的光学性质,其介电函数在垂直极化方向为半导体特性,而在平行极化方向为金属特性.在外加电场的作用下,BAGNRs的介电函数、吸收系数、折射系数、反射系数、电子能量损失系数和光电导率,其峰值向低能量区域移动,即产生红移现象.电场增强了能带间的跃迁几率.纳米带宽度对这些光学性质参数具有不同程度的影响.研究结果解释了电场调控BAGNRs光学性质的规律和微观机理.     

Fe, S共掺杂SnO2材料第一性原理分析

本文采用基于第一性原理的全电势线性缀加平面波(FP-LAPW)法, 计算了Fe, S两种元素共掺杂SnO₂材料的电子结构和光学性质. 结果表明: 材料仍为直接禁带半导体, 体系呈现半金属性; Fe, S共掺可以窄化带隙, 且随S浓度增加, 态密度向低能方向移动, 带隙减小; 共掺体系电荷密度重新分布, 随S浓度增加, Fe原子极化程度增强, 原子间键合能力增强. 共掺后介电函数虚部谱与光学吸收谱各峰随S浓度增加而发生红移, 光学吸收边减小.     

单层MoSe2单晶的光学及电学性能探究

采用Au箔作为生长衬底,通过化学气相沉积法制备了高质量的单层MoSe₂单晶.通过光学显微镜、扫描电子显微镜、扫描透射电子显微镜等对其形貌和结构进行了表征,研究了单层MoSe₂单晶的光学及电学特性.结果表明：单层MoSe₂具有非线性光学特性,并具有直接带隙结构(带隙宽度约为1.56 eV)及较好的光致发光特性.当其作为场效应晶体管器件的半导体沟道材料时,器件的载流子迁移率为1.6 cm²/(V·s),开关比约为10⁴.     

锰掺杂二硅化铬电子结构和光学性质的第一性原理计算

采用基于第一性原理的密度泛函理论(DFT)赝势平面波方法计算了锰掺杂二硅化铬(CrSi2)体系的能带结构、态密度和光学性件质.计算结果表明末掺杂CrSi2属于间接带隙半导体间接带隙宽度△ER=0.35 eV;Mn掺杂后费米能级进入导带,带隙变窄,且间接带隙宽度△Eg=0.24 eV,CrSi2转变为n型半导体.光学参数发生改变,静态介电常数由掺杂前的ε1(O)=32变为掺杂后的ε1(O)=58;进一步分析了掺杂对CrSi2的能带结构、态密度和光学性质的影响,为CrSi2材料掺杂改件的研究提供r理论依据.     

二维Ag2S的电子和光电性能的第一性原理研究

二维Ag₂S是一种具有间接宽带隙的半导体材料，由其在平面内和平面外具有独特的力学性质，因此受到了人们的广泛关注.本文基于密度泛函理论进行了第一性原理计算，研究了二维Ag₂S的电子、光学性质的变化.二维Ag₂S具有较强的方向各异性，通过不同浓度的O取代S替换掺杂，发现随着O浓度的增加，带隙值出现先增大后减小的现象;由于O元素的引入，使二维Ag₂S结构对称性降低，引起能带及光吸收、光反射的分布离散化.y方向4.56～5.36 e V处光吸收及光反射峰随掺杂浓度增加逐渐减小，且出现明显的蓝移.     

一种新型二维TiO_2的电子结构与光催化性质

基于第一性原理计算方法,设计出了一种新型二维半导体材料TiO_2,并进一步研究了其结构稳定性,电子结构,载流子迁移率和光学性质等.二维TiO_2的形成能、声子谱、分子动力学、弹性常数表明,二维TiO_2具有较好的动力学,热力学和机械稳定性,具备实验制备的条件,且能够稳定存在于常温条件下.电子结构分析表明,二维TiO_2是一种间接带隙半导体,在GGA+PBE和HSE06算法下的能隙分别为1.19 e V和2.76 e V,其价带顶和导带底能级分别由Ti-3d和Ti-4s态电子构成, O原子的电子态在费米能级附近贡献很小,主要分布在深处能级.载流子迁移率显示,二维TiO_2的迁移率比单层Mo S2要小,其电子和空穴迁移率分别为31.09和36.29 cm~2·V~(–1)·s~(–1).由于空穴迁移率和电子迁移率的各向异性,电子-空穴复合率较低,使得单层TiO_2的使用寿命更长,光催化活性更好.在应变调控下,二维TiO_2的能隙发生明显响应,以适用于各种半导体器件的需要.半导体的带边势和光学性质显示,在–5%—2%单/双轴应变下,二维TiO_2能够光裂水制H2,在–5%—5%单/双轴应变下,能够光裂水制O_2, H_2O_2和O_3等.此外,二维TiO_2对可见光和紫外光具有较高的吸收系数,说明其在未来光电子器件和光催化材料领域有着潜在的应用前景.     

第一性原理计算N掺杂对InNbO_4电子结构的影响

宽带隙(3.83 e V)半导体光催化材料InNbO_4在紫外光作用下具有分解水和降解有机物的性能.最近实验发现了N掺杂InNbO_4具有可见光下分解水制氢的活性.为了从理论上解释这一实验现象,本文采用基于密度泛函理论的第一性原理计算了N掺杂对InNbO_4的能带结构、态密度和光学性质的影响.分析能带结构可得,N掺杂后在InNbO_4的价带(O 2p)上方形成N 2p局域能级,导致电子跃迁所需的能量减小.吸收光谱表明,N掺杂后InNbO_4的光吸收边出现了红移,实现了可见光吸收.     

太阳能材料CuInS_2的晶体结构、电子和光学特性(英文)

用全电势线性缀加平面波法加局域轨道方法调查了黄铜矿半导体CuInS2的结构、电子和光学特性.我们计算的带隙0.17eV是直接的,其它实验和理论也表明这种材料有一个直接带隙.在In 4d和S3p轨道之间有相当强的杂化,构成了(InS2)4-阴离子.我们计算的反射率光谱,介电函数的实部和虚部,消光系数和折射率和实验结果取得了很好的一致.     

应力调控对单层TiOCl2电子结构及光学性质的影响

基于密度泛函理论的第一性原理计算,对单层TiOCl₂的电子结构、输运性质和光学性质进行了理论研究.对单层TiOCl₂材料的声子谱、分子动力学和弹性常数的计算结果表明,该材料在常温下能稳定存在,并具有较好的动力学、热力学和机械稳定性.电子结构分析表明,单层TiOCl₂是一种间接窄带隙半导体(能隙为1.92 eV).在应力调控下,单层TiOCl₂材料的能带结构、输运性质和光学性质均发生明显变化.沿a方向施加-4%的收缩应力后,单层TiOCl₂由间接带隙变为直接带隙,带隙减小至1.66 eV.同时TiOCl₂还表现出明显的各向异性特征,电子沿b方向传输(迁移率约为803 cm~2·V^-1·s^-1),空穴则沿a方向传输(迁移率约为2537 cm~2·V^-1·s^-1).此外,施加收缩应力还会使单层TiOCl₂材料的光吸收率、反射率和透射率的波峰(谷)发生红移...     

太阳能材料CuInS2的晶体结构、电子和光学特性

用全电势线性缀加平面波法加局域轨道方法调查了黄铜矿半导体CuInS2的结构、电子和光学特性。我们计算的带隙0.17 eV是直接的,其它实验和理论也表明这种材料有一个直接带隙。在 In 4d和S 3p轨道之间有相当强的杂化,构成了(InS2)4-阴离子。我们计算的反射率光谱,介电函数的实部和虚部,消光系数和折射率和实验结果取得了很好的一致。     

点缺陷对单层MoS2电子结构及光学性质的影响研究

采用基于第一性原理的贋势平面波方法,对不同类型点缺陷单层MoS2电子结构、能带结构、态密度和光学性质进行计算。计算结果表明：单层MoS2属于直接带隙半导体,禁带宽度为1.749ev,V-Mo缺陷的存在使得MoS2转化为间接带隙Eg=0.671eV的p型半导体,V-S缺陷MoS2的带隙变窄为Eg=0.974eV,S-Mo缺陷的存在使得MoS2转化为间接带隙Eg=0.482eV; Mo-S缺陷形成Eg=0.969eV直接带隙半导体,费米能级上移靠近价带。 费米能级附近的电子态密度主要由Mo的4d态和s的3p态电子贡献。光学性质计算表明：空位缺陷对MoS2的光学性质影响最为显著,可以增大MoS2的静态介电常数、折射率n0和反射率,降低吸收系数和能量损失。     

First-principles study of the optical properties of defect electronic structure and chalcopyrite CdGa2Te4

<正>The electronic and optical properties of the defect chalcopyrite CdGa₂Te₄ compound are studied based on the first-principles calculations.The band structure and density of states are calculated to discuss the electronic properties and orbital hybridized properties of the compound.The optical properties,including complex dielectric function,absorption coefficient,refractive index,reflectivity,and loss function,and the origin of spectral peaks are analysed based on the electronic structures.The presented results exhibit isotropic behaviours in a low and a high energy range and an anisotropic behaviour in an intermediate energy range.     

Pressure and temperature induced structural,electronic and thermal properties of CdAl2Se4

We present a comprehensive computational study on the ground state properties of CdAl₂Se₄; a defect chalcopyrite compound. Considering its potential application, we have calculated the electronic band structures using the full potential linear augmented plane wave method within the density functional theory at ambient conditions and higher pressure and temperatures. The obtained Density of states at ambient conditions compares favourably with the available experimental and theoretical results. Our calculated band gap is in excellent agreement with experimental results. Thermal effects are obtained employing quasi-harmonic Debye model. The changes in properties associated with the electronic structure of CdAl₂Se₄ are evaluated at various temperatures and pressures.     

The electronic structure,electronic charge density and optical properties of the diamond-like semiconductor Ag2ZnSiS4

The electronic structure, electronic charge density and optical properties of the diamond-like semiconductor Ag₂ZnSiS₄ compound with the monoclinic structure have been investigated using a full-relativistic version of the full-potential augmented plane-wave method based on the density functional theory, within local density approximation (LDA), generalized gradient approximation (GGA), Engel–Vosko GGA (EVGGA) and modified Becke Johnson (mBJ) potential. Band structures divulge that this compound is a direct energy band gap semiconductor. The obtained energy band gap value using mBJ is larger than those obtained within LDA, GGA and EVGGA. There is a strong hybridization between Si-s and S-s/p, Si-p and Zn-s, Ag-s/p and Zn-s, and Ag-s and Ag-p states. The analysis of the site and momentum-projected densities shows that the bonding possesses covalent nature. The dielectric optical properties were also calculated and discussed in detail.     

Mechanical stability and optoelectronic behavior of BeXP2 (X=Si and Ge) chalcopyrite

We have conducted a first-principles study on the structural, electronic, optical and elastic properties of BeSiP₂ and BeGeP₂ chalcopyrite compounds. Using the density functional theory (DFT), implemented in both full potential linear muffin-tin orbital (FP-LMTO) and Vienna Ab initio simulation (VASP) packages. The FP-LMTO is used for the determination of the structural, electronic and optical properties, while the VASP is used to determine the elastic constants that give indications about the material stability. The obtained equilibrium structural parameters are in good agreement with available results. An investigation of the band gap indicates that our compounds possess a semiconductor behavior with direct band gap for BeSiP₂ and with an indirect band gap for BeGeP₂. The energy band gaps decreased by changing Be atoms from Si to Ge. We have calculated the dielectric function ε(ω). The obtained results show that these materials are promising semiconductors for photovoltaic applications. For the elastic properties, the single-crystal elastic constants C_ij, shear anisotropic factors A, as well as polycrystalline bulk, shear and Young's modulus (B, G and E) and Poisson's ratio v have been predicted. The generalized elastic stability criteria for a tetragonal crystal are well satisfied, indicating that BeSiP₂ and BeGeP₂ are mechanically stable in the chalcopyrite structure.     

First-principles investigation of electronic structure,effective carrier masses,and optical properties of ferromagnetic semiconductor CdCr_2S_4

The electronic structures, the effective masses, and optical properties of spinel CdCr_2S_4 are studied by using the fullpotential linearized augmented planewave method and a modified Becke–Johnson exchange functional within the densityfunctional theory. Most importantly, the effects of the spin–orbit coupling(SOC) on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center.SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr_2S_4. These should be useful to deeply understand spinel CdCr_2S_4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications.     

Density functional theory analysis of electronic structure and optical properties of La-doped Cd_2SnO_4 transparent conducting oxide

The electronic structural, effective masses of carriers, and optical properties of pure and La-doped Cd_2SnO_4 are calculated by using the first-principles method based on the density functional theory. Using the GGA+U method, we show that Cd_2SnO_4 is a direct band-gap semiconductor with a band gap of 2.216 eV, the band gap decreases to 2.02 e V and the Fermi energy level moves to the conduction band after La doping. The density of states of Cd_2SnO_4 shows that the bottom of the conduction band is composed of Cd 5 s, Sn 5 s, and Sn 5 p orbits, the top of the valence band is composed of Cd 4d and O 2p, and the La 5 d orbital is hybridized with the O 2 p orbital, which plays a key role at the conduction band bottom after La doping. The effective masses at the conduction band bottom of pure and La-doped Cd_2SnO_4 are 0.18 m0 and 0.092 m_0, respectively, which indicates that the electrical conductivity of Cd_2SnO_4 after La doping is improved. The calculated optical properties show that the optical transmittance of La-doped Cd_2SnO_4 is 92%, the optical absorption edge is slightly blue shifted, and the optical band gap is increased to 3.263 eV. All the results indicate that the conductivity and optical transmittance of Cd_2SnO_4 can be improved by doping La.