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．     

Electronic properties of boron nanotubes with axial strain

The electronic properties of boron nanotubes with axial strain are investigated by first principle calculations. The band gaps of the (3, 3) and (5, 0) boron nanotubes are found to be modified by axial strain significantly. We find that the semiconductor-metal transition occurs for the (3, 3) boron nanotubes with both compressive and tensile strain. While for the (5, 0) boron nanotubes, only the tensile strain induces the semiconductor-metal transition. These boron nanotubes have the largest gaps under compressive strain.      

Microstrip microwave band gap structures

Microwave band gap structures exhibit certain stop band characteristics based on the periodicity, impedance contrast and effective refractive index contrast. These structures though formed in one-, two- and three-dimensional periodicity, are huge in size. In this paper, microstrip-based microwave band gap structures are formed by removing the substrate material in a periodic manner. This paper also demonstrates that these structures can serve as a non-destructive characterization tool for materials, a duplexor and frequency selective coupler. The paper presents both experimental results and theoretical simulation based on a commercially available finite element methodology for comparison.      

利用透射系数研究周期势的能带结构

利用一维方位势透射系数的递推公式研究了周期势的能带结构,文中考察了能 结构与垒宽、阱宽及位势个数的关系。     

Photoacoustic determination of energy band gap of semiconductors

Semiconducting materials are employed in the fabrication of a number of semiconductor devices and opto-electronic detectors etc depending on their properties, state of purity and perfection and energy band gap values. In the present study, a latest and novel photoacoustic spectroscopic technique has been employed for the determination of energy band gap of some semiconductors namely CdS, CdSe, CdTe, ZnS, ZnO, Se and Si in the powder form. Values obtained have been compared with those reported by conventional methods.     

Electronic structure of ZnO wurtzite quantum wires

The electronic structure and optical properties of ZnO wurtzite quantum wires with radius R≥3 nm are studied in the framework of six-band effective-mass envelope function theory. The hole effective-mass parameters of ZnO wurtzite material are calculated by the empirical pseudopotential method. It is found that the electron states are either two-fold or four-fold degenerate. There is a dark exciton effect when the radius R of the ZnO quantum wires is in the range of [3,19.1] nm (dark range in our model). The dark ranges of other wurtzite semiconductor quantum wires are calculated for comparison. The dark range becomes smaller when the |Δ_so| is larger, which also happens in the quantum-dot systems. The linear polarization factor of ZnO quantum wires is larger when the temperature is higher.     

Thermal stress induced band gap variation of ZnO thin films

The growth temperature and post annealing-dependent optical and structural effect of RF magnetron sputtered ZnO thin films were examined. As the growth temperature increased, the lattice constant increased and approached the bulk value, suggesting a decrease in interfacial strain between the substrate and thin film. For the post annealed samples, the interfacial strain decreased further and was close to the bulk value regardless of the post annealing environments (in air and O₂). The optical properties of all ZnO thin films examined and revealed higher transparency (>90%). Furthermore, the optical band gap varied according to the growth temperature and post annealing environments due to a decrease in the interfacial strain effect.     

FeS2能隙的外压微扰调制

 采用基于密度泛函理论的自洽赝势方法,计算了FeS₂在外压调制下的电子结构性质。计算结果表明：随着压缩度的增加,外压调制下的Fe—S键长缩短,FeS₂小的能隙变宽,Fe的d电子与S的p电子杂化增强,原子间相互作用增大。这一能隙随压力增大而增大的结果,与非导体在高压下金属化的特征相反。     

Low frequency phononic band structures in two-dimensional arc-shaped phononic crystals

The low frequency phononic band structures of two-dimensional arc-shaped phononic crystals (APCs) were studied by the transfer matrix method in cylindrical coordinates. The results showed the first phononic band gaps (PBGs) of APCs from zero Hz with low modes. Locally resonant (LR) gaps were obtained with higher-order rotation symmetry, due to LR frequencies corresponding to the speeds of acoustic waves in the materials. These properties can be efficiently used in a structure for low frequencies that are forbidden, or in a device that permits a narrow window of frequencies.     

电子密度对等离子体光子晶体禁带特性的影响

从Maxwell方程出发,采用类似于量子力学Kronig-Penney模型求解周期势的方法,结合双水电极介质阻挡放电的实验结果,研究了电子密度ne对一维等离子体光子晶体禁带特性的影响。研究发现:电子密度对等离子体光子晶体光子禁带的位置和宽度均有重要的影响;等离子体光子晶体的禁带宽度随电子密度的增加而增大,增长速率为电子密度的函数;等离子体光子晶体的截止频率、光子禁带边缘频率随电子密度的增大而增大。给出了当等离子体光子晶体具有显著禁带宽度时的电子密度的理论临界值。     

Comparison of wurtzite atomistic and piezoelectric continuum strain models: Implications for the electronic band structure

We compare continuum and atomistic models for the electromechanical fields in wurtzite GaN/AlN quantum dots and their relative impact on the electronic band structure. Qualitative agreement between atomistic strain calculations and continuum elastic models for a wurtzite hexagonal quantum-dot structure is demonstrated; however, significant quantitative discrepancies of up to 100 meV are observed. A smaller difference of approximately 15 meV is found between fully coupled and semi-coupled continuum models.     

Ab initio electronic band structure calculation of InP in the wurtzite phase

We present ab initio calculations of the InP band structure in the wurtzite phase and compare it with that of the zincblende phase. In both calculations, we use the full potential linearized augmented plane wave method as implemented in the WIEN2k code and the modified Becke-Johnson exchange potential, which provides an improved value of the bandgap. The structural optimization of the wurtizte InP gives , , and an internal parameter u=0.371, showing the existence of a spontaneous polarization along the growth axis. As compared to the ideal wurtzite structure (that with the lattice parameter derived from the zincblende structure calculations), the actual wurtzite structure is compressed (−1.3%) in plane and expanded (0.7%) along the c-direction. The value of the calculated band gaps agrees well with recent optical experiments. The calculations are also consistent with the optical transitions found using polarized light.     

Electronic structure of La2CuO4

The electronic band structure of La₂CuO₄ is performed using self-consistent linear muffin-tin orbital method. The 17 band complex is found to arise mainly from the overlap between Cu-3d and O-2p wavefunctions. The calculated density of states at the Fermi energy (N E _F), the conduction band-width and the electronic specific heat coefficient are given.     

Design and optimisation of multimode 1d photonic band gap waveguide

The modal characteristics of planar waveguides with photonic band gap guiding properties are studied. It is demonstrated that a slight deviation from the periodicity in the photonic band gap multilayers can result in multimode transmission within the guiding layer. Possible applications of the results for avoiding single mode regime destruction due to fabrication process imperfection, as well as for designing such waveguides for conventional and emerging new applications of multimode photonic devices, are pointed out.     

Room temperature near-field photoluminescence of zinc-blend and wurtzite ZnO structures

Near-field photoluminescence (PL) was measured from ZnO film, composed of nanocrystallites with zinc-blend (ZB) and wurtzite (W) structures, on a sapphire (0 0 0 1) substrate at room temperature (RT). The size of nanocrystallites was in the range of 30–50 nm. Using a fiber probe with aperture size of 80 nm, two near-field emission peaks attributed to one ZB and one W structures were observed. The difference in the emission energies was 0.10 eV close to the calculated bandgap difference between ZB and W structures. The intensity of emission peak from ZB structure with lower energy was stronger than that from W structure, which is supposed to be resulted from the quenched excitonic effect of W structure.     

Design and optimisation of multimode 1D photonic band gap waveguide

The modal characteristics of planar waveguides with photonic band gap guiding properties are studied. It is demonstrated that a slight deviation from the periodicity in the photonic band gap multilayers can result in multimode transmission within the guiding layer. Possible applications of the results for avoiding single mode regime destruction due to fabrication process imperfection, as well as for designing such waveguides for conventional and emerging new applications of multimode photonic devices, are pointed out.     

First-principles energy band calculation for undoped and S-doped TiO2 with anatase structure

The electronic structure of S-doped TiO₂ with an optimized anatase structure was calculated within the framework of the density functional theory (DFT). For the calculation we built four kinds of supercells; type-A and B supercells consist of 12 and 48 atoms and a centered Ti atom is substituted for an S atom, while type-C and D supercells consist of 12 and 48 atoms and a centered O atom is substituted for an S atom. The supercells (type-B and D) were employed to adjust the S-concentration in TiO₂ to an experimental value of a few %. The changes of the lattice parameters are not significant in the type-A and B supercells. The phase transition from the tetragonal to the orthorhombic occurs in the type-C and D supercells. In the small supercell (type-A), S-related states are located in the range of −1.6 to 0 eV, and the S-states are band-like. In contrast, in the large supercell (type-B), S-related states appeared at about 0.9 eV above the top of the valence band, and the S-states are atomic-like. The localization of the S-related states is remarkable in the type-B supercell. In the type-D supercell, the S-related states were merged with the top of the valence band, and as a result the band-gap energy is narrowed by 0.7 eV. Despite a low S-concentration (3%) in the type-D supercell, the S-related states are somewhat band-like.     

一维等离子体光子晶体的带隙研究

采用时域有限差分方法(FDTD),结合等离子体计算中的分段线性电流密度卷积技术(PLJERC)对一维等离子体光子晶体(1D-PPC)进行了数值模拟,给出了微分高斯脉冲在一维等离子体光子晶体中的传播过程。计算得到的带隙结构与K-P模型方法的结果一致。计算并分析了等离子体频率、介质介电常数、等离子体-介质层的厚度比以及周期厚度对一维等离子体光子晶体带隙结构的影响。     

Fabrication and optical properties of 3D composite photonic crystals of core-shell structures

Three-dimensional (3D) composite colloidal photonic crystals with SiO₂ core and ZnO shell were fabricated on borosilicate glass (BSG) substrate by a two-stage deposition method. Scanning electron microscopy (SEM) measurements show that both the pre-deposited SiO₂ and SiO₂/ZnO core-shell structures are oriented with their (1 1 1) axes parallel to the substrates. Optical measurement reveals that the periodic arrays exhibit a photonic band gap in the (1 1 1) direction. The optical properties of SiO₂/ZnO core-shell structures strongly depend on the size dispersions of colloidal spheres and the intrinsic defects in the sample.