C掺杂GaAs外延层光学特性分析

对利用EMCORE D125 MOCVD系统生长的以CCl4为掺杂源,分析不同C掺杂浓度的GaAs外延层光学特性.通过PL、DC XRD测试手段研究了掺C GaAs层,随C掺杂浓度增加,禁带宽度收缩,PL谱峰值半宽增大,晶格常数减小.     

锰掺杂对钛酸锶铅铁电薄膜带-带跃迁和带尾吸收特性的影响

通过透射光谱研究了锰掺杂量对钛酸锶铅铁电薄膜光学特性尤其是带-带跃迁和带尾吸收特性的影响,并利用柯西色散关系获得了光学透明区的光学常数.研究表明:随着锰掺杂量的增加,钛酸锶铅铁电薄膜的禁带宽度减小而带尾能增加.禁带宽度随锰掺杂的收缩可以归因为锰3d轨道降低了导带底的能级及掺杂后晶格的减小.掺杂锰离子的随机占位和非等价掺杂后氧空位浓度的增加则是导致局域带尾态拓宽的主要原因.     

锰掺杂对钛酸锶铅铁电薄膜带-带跃迁和带尾吸收特性的影响（英文）

通过透射光谱研究了锰掺杂量对钛酸锶铅铁电薄膜光学特性尤其是带-带跃迁和带尾吸收特性的影响,并利用柯西色散关系获得了光学透明区的光学常数.研究表明:随着锰掺杂量的增加,钛酸锶铅铁电薄膜的禁带宽度减小而带尾能增加.禁带宽度随锰掺杂的收缩可以归因为锰3d轨道降低了导带底的能级及掺杂后晶格的减小.掺杂锰离子的随机占位和非等价掺杂后氧空位浓度的增加则是导致局域带尾态拓宽的主要原因.     

n-ZnO／p-GaN异质结界面工程

宽禁带直接带隙半导体材料ZnO与GaN在晶体结构、晶格常数以及能带宽度等方面具有非常相似的特性。ZnO在高自由激子结合能（60meV）、适于湿法刻蚀以及对环境友好等方面具有优势，在短波长低阈值发光二极管（LED）以及激光二极管等方面具有广阔的应用前景。但ZnO在稳定的P型掺杂方面遇到很大的挑战，高亮度ZnO同质结型发光二极管的制作具有很大的难度。     

Ag-N共掺杂ZnO电子结构的理论研究

采用基于DFT理论的第一性原理方法研究了Ag-N共掺杂纤锌矿ZnO的晶格结构和电子结构,计算了包括共掺杂体系的晶格常数、杂质形成能和电子态密度等性质。研究结果显示,共掺改善了杂质原子对体相晶格结构的扰动,提高了掺杂的稳定性。此外,电子结构的计算表明共掺形成的受主能级较单掺时更浅,且空穴态的局域性降低,从而改善了p型ZnO的传导特性,表明受主共掺可能是一种比较有潜力的p型ZnO掺杂方式。计算与实验结果符合,为受主共掺形成p型ZnO的机理提供了理论支持。     

CrO共掺杂对GaN电子结构和光学性质的影响

利用第一性原理方法研究了O、Cr和CrO共掺杂对宽禁带半导体材料GaN的结构、能带和光学性质的影响.结果表明CrO共掺的方法可以在原GaN晶体中产生中间能带,CrO共掺的方法较单个氧原子掺杂可以降低材料的形成能.中间能带的出现实现了材料对低能光子的吸收,增强了其对太阳光谱中红外波段的能量利用,从理论上预言CrO共掺Ga...     

S掺杂CuInSe2:导致的体积变化对其禁带宽度的影响

运用第一性原理方法研究了CulnSe2和不同量的S掺杂CulnSe2所形成的化合物的电子结构.理论计算表明,S掺杂导致CuInse2禁带宽度增大,且通过对其电子结构和键长的分析,发现因S掺杂浓度的增加而导致的CulnSeS化合物晶格体积减小对其禁带宽度的增加有重要的影响.     

S掺杂CuInSe2导致的体积变化对其禁带宽度的影响

运用第一性原理方法研究了CuInSe2和不同量的S掺杂CuInSe2所形成的化合物的电子结构. 理论计算表明,S掺杂导致CuInSe2禁带宽度增大,且通过对其电子结构和键长的分析,发现因S掺杂浓度的增加而导致的CuInSeS化合物晶格体积减小对其禁带宽度的增加有重要的影响.     

用EHMO方法计算晶体电子态密度的一种改进

本文讨论Si集团的EHMO计算.适当选择参数k可使集团总能量当晶格常数a=5.42A|°(即硅的晶格常数)时为最小.在基函数中引进Si-3d轨道后,便可改进集团计算的禁带宽度.     

单Mo和Mo/S共掺杂锐钛矿相TiO_2的电子结构计算

利用基于密度泛函理论的第一性原理计算了Mo单掺杂和Mo/S共掺杂锐钛矿相TiO2的能带结构、电子分态密度、电子密度和吸收光谱。结果表明,Mo单掺杂在锐钛矿相TiO2导带底下方引入了两条主要由Mo 4d轨道组成的掺杂能级,而Mo/S共掺杂在TiO2的禁带之内共引入了四条掺杂能级,位于价带顶上方的两条主要由S 3p轨道组成,而位于导带底下方的两条掺杂能级则主要由Mo 4d和S 3p轨道杂化形成。Mo单掺杂和Mo/S共掺杂分别使TiO2的禁带宽度增大0.36 eV和0.43 eV,从而出现吸收带边的蓝移。电子密度图表明,Mo单掺杂对TiO2的晶格影响较小,但Mo/S共掺杂则使TiO2的晶格畸变程度加大。     

Ag掺杂ZnO/GaN异质结可见光吸收特性的第一性原理

ZnO/GaN异质结带隙宽度较宽,制约了对可见光的吸收。为研究Ag对ZnO/GaN异质结可见光吸收的影响,在(1-100)非极性面上构建GaN/ZnO异质结,并用Ag分别取代不同位置的Zn和Ga原子,采用第一性原理计算Ag掺杂对ZnO/GaN异质结稳定性、电子结构、光学性质和带边位置的影响。研究结果表明：Ag掺杂ZnO/GaN异质结形成能为负值,结构稳定;Ag置换Zn和Ga使带隙宽度由2.93 eV分别减小至2.7 eV和2.3 eV,吸收系数和光电导产生红移,有利于可见光的吸收,Ag掺杂ZnO/GaN异质结具有良好的光催化活性。     

Structural and energy characteristics of native vacancy-type defects in the biaxially stressed GaN lattice

For biaxially stressed GaN clusters, the structure, charges, and energies of the formation of intrinsic Ga and N vacancies are calculated by the quantum-chemical method in the SCF MO LCAO approximation taking into account relaxation of the crystalline surroundings. It is established that the use of substrates introducing compressive or tensile stresses into the epitaxial layer affects the concentrations of intrinsic vacancy-type point defects. This effect most clearly manifests itself in the nitrogen sublattice in the GaN crystal lattice, especially in the case of its tension, i.e., during the epitaxial grown of GaN on the Si substrate. Redistribution of the electron density in the defect region in the case of lattice compression or tension can be the cause of variation in the location of electronic levels of defects in the band gap of the crystal.     

纤锌矿GaN光电性质的第一性原理研究

利用平面渡赝势密度泛函的方法,结合广义梯度近似,对纤锌矿GaN的光电性质进行了研究.对纤锌矿GaN的能带结构、态密度分布、复介电函数和吸收光谱进行了计算.文中分析了纤锌矿结构GaN晶体可能的跃迁及其对应的吸收光谱.结果显示GaN晶体的光学性质与晶体的电子结构直接相关.计算结果为进一步理解和改进纤锌矿GaN的光电性质提供理论基础.     

An ab initio study of the structural,elastic, electronic,optical properties and phonons of the double perovskite oxides Sr2AlXO6 (X=Ta,Nb, V)

We report ab initio density functional theory calculations of the structural, elastic, electronic and optical properties of the double perovskite oxides Sr₂AlXO₆ (X=Ta, Nb, V). We have predicted a direct Г–Г band gap in Sr₂AlXO₆ (X=Ta, Nb) and an indirect Г–X band gap for Sr₂AlVO₆. The fundamental band gap increases linearly when the pressure is enhanced in the range 0–20 GPa. The frequency dependent of complex dielectric function, absorption, reflectivity and electron energy loss function were investigated in the range 0–40 eV. Features such as lattice constant, bulk modulus, elastic constants, band structure, total and local densities of states have been computed.     

具有双周期势的石墨烯超晶格电子带隙和传输特性的研究

运用传输矩阵理论,研究了双周期势石墨烯超晶格(GSL)的电子带隙和传输特性。结果表明,这种准周期结构存在一个新的狄拉克点,并且它的位置恰好位于零平均波数带隙处;与传统的布拉格带隙相比,这种带隙的位置对晶格常数和入射角度的变化不敏感。讨论了入射角度对电子在双周期势中传输特性的影响,预言了双周期势中可控的电子传输过程,定量分析了允带宽度与周期总数目的幂指数关系。     

4H-SiC中点缺陷的第一性原理研究

基于密度泛函理论和第一性原理,对4H-SiC晶格中5种点缺陷(VC,VC-C,填隙B,替位B和替位P)的晶格常数、电荷布居、能带等微观电子结构进行了计算,并从缺陷形成能、杂质电离能和载流子浓度等角度分析了这些点缺陷对材料性能的影响.计算结果表明:在这些点缺陷中,C空位的形成能最低,仅为5.929 1 eV,属于比较容易形成的一类点缺陷.同时在能带图中可以看到填隙B的禁带中央附近出现了一条新能带,这条新能带的产生促使填隙B成为5种缺陷中禁带宽度最小的缺陷,有利于SiC半导体器件中载流子的输运.在3种杂质点缺陷中,替位P的电离能最小.掺杂杂质电离能越小,电离程度越深,产生的载流子浓度也越大,这一结论在载流子浓度的计算结果中也得到了验证.     

Hybrid n-GaN and polymer interfaces: Model systems for tunable photodiodes

Hybrid optoelectronic device structures offer promising options for a wide range of properties. The functioning of hybrid-bilayer devices is largely determined by their interface. Hybrid-bilayer devices based on wide band gap gallium nitride (GaN) and low band-gap donor/acceptor polymers offer a unique combination and model interface systems for application in photodetectors. A systematic study of the optoelectronic properties, specifically the photocurrent as a function of voltage bias and incident wavelength, has been carried out for n-Gan/polymer bilayer structures. A clear evidence of interface polarization originating from the GaN surface manifests in the current–voltage characteristics and photocurrent response of the hybrid structure.     

Nanometer-scale studies of nitride/arsenide heterostructures produced by nitrogen plasma exposure of GaAs

We have investigated the nanometer-scale structure and electronic properties of nitride/arsenide superlattices produced by nitridation of a molecular beam epitaxially grown GaAs surface. Using cross-sectional scanning tunneling microscopy and spectroscopy, we find that the nitrided layers are not continuous films, but consist of groups of atomic-scale defects and larger clusters. We identify the defects and clusters as N_As and GaN with dilute As concentration, respectively. Thus, the nitrided regions consist of alloys from both sides of the miscibility gap predicted for the GaAsN system. In addition, spectroscopy on the clusters reveals an upward shift of the band edges and band gap narrowing, with significant change in the conduction band structure. We estimate the contribution of strain to band gap narrowing in terms of an elasticity calculation for a coherently strained spherical GaN cluster embedded in GaAs.     

Phase transition and related electronic and optical properties of crystalline phenanthrene: An ab initio investigation

This investigation discusses a structural phase transition of organic crystalline phenanthrene and the resulting changes of its electronic and optical properties investigated by ab initio calculations based on density functional theory (DFT). The structure of phase I has been optimized then its electronic and optical properties have been calculated. Our computational results on phase I (at ambient pressure) get along well with the available experimental data.Calculating the electronic and optical properties of phase II are proceeded in the same way and the results, particulary Raman spectra, reveal a crystallographic phase transition indicated by abrupt changes in lattice constants which are accompanied by rearrangement of the molecules. This results in modifications of the electronic structure and optical response. For both phases the band dispersion of the valence and conduction bands are anisotropic, whereas the band splitting is strongly noticeable in phase II. By calculating the imaginary part of the dielectric function of phase II, we have found the appearance of new peaks at the lowest z-polarized absorption and about 30 eV in all absorption components. Excitonic effects in the optical properties of phases I and II have been investigated by solving the Bethe–Salpeter equation (BSE) on the basis of the FPLAPW method. Phase II shows four main excitonic structures in the energy range below band gap, whereas phase I shows two. The excitonic structures in the optical spectra of phase II show a red shift in comparison to phase I. The calculated binding energies of spin-singlet excitons in phase II are larger than the ones in phase I.