大带隙二维三角格子光子晶体结构参数的优化设计

光子晶体结构设计优化是理论研究的一个重要内容.运用平面波展开法对圆柱、方柱及正六边柱构造的二维三角格子光子晶体的禁带进行仿真计算,讨论了介质材料分别为GaAs、Si和Ge情况下,柱子形状、旋转角度、填充比的变化对完全光子禁带的影响.发现:对于二维三角格子光子晶体,相对于介质柱,空气柱更易获得完全光子禁带;而相对于圆柱及...     

三维光子晶体典型结构完全禁带的最佳参数理论分析

基于平面波展开法，理论分析了晶格结构、填充率、介电常数比等因素对fcc，diamond，woodpile三种三维光子晶体典型结构完全禁带的影响.三种结构中，fcc结构由于高对称性导致的能级简并，只适用于密堆积排列的反蛋白石结构；diamond结构非常容易产生高带隙率的完全禁带，并且可以通过调节多项参数得到所需的完全禁带；woodpile结构参数调节范围比较宽，为实验制备带来方便.对于不同的三维光子晶体结构，随着介电常数比的增大，完全禁带的宽度和带隙率也会随着增大.还发现了一些以前未引起注意的现象. 关键词： 三维光子晶体 完全禁带 介电常数比 带隙率 平面波展开法     

光子晶体液体浓度传感器

为了有效地检测混合液体的浓度,运用平面波展开法与光子晶体禁带理论,研究了光子晶体禁带宽度和混合液体浓度的对应关系。以砷化镓(GaAs)为背景材料的三角格子空气孔二维光子晶体内分别填充不同浓度的水醋酸、水甲醇混合液体,讨论了混合液体浓度与介电常数对二维光子晶体禁带宽度的影响。模拟结果表明,在温度保持不变的情况下,浓度在0～0.60mol/kg之间变化时二维光子晶体TE模没出现光子晶体禁带而TM模出现的光子晶体禁带宽度随着混合液体浓度和介电常数的增大而逐渐变窄且向高频区域移动。这一结果为生物化学中混合液体浓度的检测方面提供很好的参考依据。     

低频和高频区域内大禁带的二维各向异性光子晶体

采用一种改进的平面波展开法,运用一种有效的设计二维各向异性光子晶体的方法,在低频和高频区域内获得了具有较大禁带的两种二维光子晶体.低频区域内,找到具有最大禁带宽度的光子晶体的禁带宽度为Δω=0076(2πca),中心频率为0769(2πca)(这里的a为晶格常量).高频区域内,找到的光子晶体的最大禁带宽度为Δω=01(2πcα),中心频率为1653(2πca).同时在低频区域内,发现一种很简单的正方网格结构,它的禁带宽度为Δω=00574(2πca),禁带宽度与禁带的中心频率之比为Δωωc=11782%. 关键词： 光子晶体 平面波展开法 各向异性材料 完全禁带     

光学材料 光学晶体、液晶

O734 2005032257 完全禁带二维光子晶体的研究=Two dimensional photon- ic crystals with complete band gaps[刊,中]／张磊(中科院 光电所微细加工光学技术国家重点实验室．四川,成都 (610209)),张晓玉…∥半导体光电．-2004,25(6)．- 480-483 利用平面波展开法,对存在完全禁带的正三角排列的 气柱型二维光子晶体和蜂窝状排列的介质柱型二维光子 晶体进行了研究,分析了柱的半径和介质折射率对完全禁 带大小的影响。结果表明,正三角排列气柱型比蜂窝状排     

空气环型二维光子晶体完全带隙特性研究

采用平面波展开法, 系统研究了空气环型二维光子晶体的完全光子带隙随结构参数变化而改变的规律, 并将其与普通的空气孔型和介质柱型二维光子晶体的完全带隙进行了比较. 研究表明: 空气环型二维光子晶体不仅可以获得更宽的完全带隙, 而且, 当介质折射率较低时, 其可以获得普通空气孔型和介质柱型二维光子晶体在低折射率条件下所无法获得的完全带隙. 关键词： 空气环型二维光子晶体 完全带隙 平面波展开法     

二维正方晶格光子晶体禁带特性

基于平面波展开法,以碳化硅构成二维正方晶格光子晶体,数值模拟了TE模、TM模二维光子晶体的禁带特性,结果表明,TE模更容易形成光子禁带。同时设计了以碳化硅构成二维正方晶格光子晶体波导,数值模拟了TE模、TM模波导的传输特性和禁带特性,结果表明,TE模构成的波导电磁波能够较好的传播,它们的光子禁带都没有出现。研究结论为光子晶体波导器件的开发提供参考。     

二维介质柱型Archimedes(4,8~2)复式晶格光子晶体禁带特性研究

采用平面波展开法分别模拟了空气背景下由介质圆柱和方柱构造的二维Archimedes(4,82)复式晶格光子晶体的能带结构,讨论了介质柱形状、折射率、填充比和旋转对称性等因素对完全光子禁带的影响.研究发现,当折射率在2.60到5.40之间时,介质圆柱和方柱构造的二维Archimedes(4,82)复式晶格光子晶体都出现了完全光子禁带.随着折射率的增大,最大完全禁带宽度并非随之增大而是存在峰值,介质圆柱型晶格在折射率为2.80时出现峰值;介质方柱型晶格在折射率为2.80和4.40两处出现峰值,且旋转介质方柱能够明显增大禁带宽度,同时存在最佳旋转角度.分析结果表明,在最大完全禁带处,折射率、填充比以及旋转角度等因素的变化对禁带特性的影响很小.     

2维光子晶体中的掺杂效应数值研究

 把平面波展开方法(PWM)用于2维光子晶体掺杂情况下透射特性的研究,计算得到了粗细不同的空气柱掺杂、相同半径不同介质柱掺杂、不同柱体形状掺杂情况下2维光子晶体的透射系数与入射光频率的关系曲线。结果表明2维光子晶体的禁带的宽度、位置、透过率与掺杂体半径、掺杂体介电常数、掺杂体柱体几何形状等因素有关,掺杂因素相差越大透射曲线变化越明显,特别是损耗介质的掺入更使得禁带可调要素增加。     

介质柱型二维Triangular格子光子晶体的禁带特性

采用平面波展开法数值计算了空气背景中由圆形、正六边形和正方形介质柱构造的二维三角晶格光子晶体禁带结构,并研究了介质方柱旋转角度、介质折射率和填充比对完全光子禁带宽度的影响.结果表明,在低频区,介质方柱旋转17°时,出现最大完全光子禁带,且最大禁带宽度随介质折射率的变化较为稳定.在高频区,介质方柱旋转30°时,完全光子禁带宽度最大;且介质材料折射率n=2.2时即出现完全光子禁带,n=2.6时,完全光子禁带达到最大.     

Photonic bandgap properties of 8-fold symmetric photonic quasicrystals

The bandgap properties of 2D 8-fold symmetric photonic quasicrystals (PQCs) composed of a set of rods are numerically investigated for various fill factors, dielectric constants and propagation angles using the finite difference time domain (FDTD) method. Some interesting properties are found besides the known results: (i) the central frequency of the bandgap shifts to low frequency as r/a increases; (ii) an optimum fill factor to obtain the largest gap width exists, which decreases with increasing dielectric constant; (iii) compared with the behavior for a given fill factor, the variation of bandgap width for the optimum fill factor increases much more significantly with the dielectric constant. Selection guidelines for 8-fold symmetric PQC designs are provided for optimum fill factors and variation of the relative bandgap width at different dielectric constants.     

Effect of Dielectric Constant Contrast and Filling Factor to Photonic Bandgap

The effect of dielectric constant contrast and the filling factor to the photonic bandgap in a 2-D square lattice photonic crystal is discussed. The location, width and number of photonic bandgap can be modulated.     

Optical properties of melamine based materials

The melamine based crystalline materials are synthesized. To determine the optical properties the transmittance and reflectance spectra are recorded. The absorption coefficient of the materials is calculated using the recorded transmittance values. From the absorption coefficient values the insulating behavior of all our studied materials is identified. In addition the direct bandgap transition nature of the materials is recognized from the absorption coefficient value. Tauc relation is used to determine the bandgap energy. The bandgap energy values suggest the dielectric nature of the materials and interpretation is given for high dielectric constant values.     

Bandgaps and band bowing in semiconductor alloys

The bandgap and band bowing parameter of semiconductor alloys are calculated with a fast and realistic approach. The method is a dielectric scaling approximation that is based on a scissor approximation. It adds an energy shift to the bandgap provided by the local density approximation (LDA) of the density functional theory (DFT). The energy shift consists of a material-independent constant weighted by the inverse of the high-frequency dielectric constant. The salient feature of the approach is the fast calculation of the dielectric constant of alloys via the Green function (GF) of the TB-LMTOs (tight-binding linear muffin-tin orbitals) in the atomic sphere approximation (ASA). When it is applied to highly mismatched semiconductor alloys (HMAs) like Zn Te_xSe_1?x, this method provides a band bowing parameter that is different from the band bowing parameter calculated with the LDA due to the bowing exhibited also by the high-frequency dielectric constant.     

Nearly isotropic photonic bandgap structures in two dimensions

It is suggested that a material with a novel spatial dielectric distribution can exhibit a bandgap that is approximately independent of propagation angle. This independence is accomplished by development of the dielectric constant from reflection vectors of equal strength that are ideally equispaced in angle.     

La掺杂3C-SiC电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法,对未掺杂及稀土材料La掺杂3C-SiC的电子结构和光学性质进行理论计算.计算结果表明,La掺杂引起3C-SiC晶格体积增大,掺杂体系能量更小,掺杂体系的结构更稳定;未掺杂3C-SiC是直接带隙半导体,其禁带宽度为1.406 eV,La掺杂后带隙宽度下降为1.161 eV,La掺杂3C-SiC引入了3条杂质能级,能量较高的1条杂质能级与费米能级发生交叠,另外2条杂质能级都在费米能级以下价带顶之上,La掺杂引起3C-SiC吸收谱往低能区移动,未掺杂3C-SiC的静态介电常数为2.66,La掺杂引起静态介电常数增加为406.01,La掺杂3C-SiC是负介电半导体材料.     

Tunability of the photoluminescence in porous silicon due to different polymer dielectric environments

In this report we demonstrate control over porous silicon (PSi) emission properties by changing the dielectric environment surrounding the silicon crystallites, as well as provide information on the effects of pore infiltration of PSi. This is achieved by making PSi–polymer nanocomposites by diffusing or polymerizing a range of varying dielectric constant polymers into the pores. The degree of modification in photoluminescence (PL) depends on the dielectric constant of the polymers. By increasing the dielectric constant of the environment surrounding the crystallites, a blue shift in PL as high as 222 meV has been observed. The blue shift is attributed to the high dielectric constant of the polymers relative to PSi, which causes a partial screening of the excitons allowing the excitonic levels to shift closer to the bandgap. The shift in excitonic levels increases when the dielectric constant of the polymer increases. PSi–polymer nanocomposites also exhibit an increase in PL intensity, which suggest that the inert infiltrated polymers are able to passivate existing nonradiative channels.     

Growth and properties of YAlO film synthesized by RF magnetron sputtering

YAlO films are synthesized on (1 0 0)-oriented Si substrates by RF magnetron sputtering method. Al₂O₃ wafer is used as a target material, and some small pieces of Y bulk material are put on the Al₂O₃ target to synthesize YAlO films. Y composition ratio is varied from 0 to 34%. Amorphous YAlO films are characterized. An electrical resistivity as high as 3.4 × 10¹⁴ Ω-cm is achieved for the YAlO film with Y composition ratio of 10%. The dielectric constant increases with increasing Y composition ratio, and the YAlO film with Y composition ratio of 34% has a dielectric constant of 10.2. The bandgap energy of the YAlO film is suggested to be wider than 6.5 eV. YAlO films with a surface roughness of 0.4-1.3 nm are obtained irrespective of the Y composition ratio.     

应变对纤锌矿结构GaN电子结构及光学性质的影响

使用第一性原理密度泛函理论（DFT）框架下的广义梯度近似（GGA+U）方法计算单轴应变对纤锌矿结构GaN的键长、差分电荷密度、电子结构以及光学性质的影响.结果表明：带隙随应变的增加而减小,压应变在（-1%~-3%）范围内变化时带隙变化不明显,压应变超过3%时带隙随应变的增大显著减小.光学性质研究表明,应变对介电函数虚部峰的位置和大小都产生影响,静态介电常数随应变的增大而增大;应变使GaN的吸收系数减小.     

二维光子晶体T型波导分支器数值模拟研究

采用平面波展开法和时域有限差分法,对GaAs二维正方晶格光子晶体的色散特性和带隙结构进行了数值模拟研究,并对GaAs二维光子晶体线缺陷构成的T型波导分支器的微波传输特性进行了模拟和优化。数值模拟结果表明,光子晶体填充比对带隙结构有显著地影响。通过在拐角处插入额外的电介质棒对GaAs二维正方光子晶体T型波导分支器进行优化,数值模拟的结果表明,优化的GaAs二维正方光子晶体T型波导分支器在一阶带隙范围内透射系数将提高到0.96以上。