含双负缺陷的一维光子晶体耦合腔的杂质带特性

利用转移矩阵方法研究了含双负缺陷的一维光子晶体耦合腔的透射谱.计算结果表明，如果改变缺陷的折射率，缺陷模之间的耦合作用将发生改变，使得能隙中的杂质带也随之改变.若这个折射率取适当值，则可以在禁带中同时出现几个尖锐的透射峰和较宽的通带，这种结构可同时用于多通道窄带滤波和宽带滤波. 关键词： 光子晶体 缺陷模 杂质带 滤波     

二维光子晶体耦合腔阵列的慢波效应研究

设计了一种六角晶格二维光子晶体耦合腔阵列,平面波展开法计算能带表明,处于禁带中的耦合缺陷腔模的色散曲线在光子晶体平面内所有k矢量方向更加平坦.模拟了横电波沿ΓK方向的透射谱.与光子晶体单缺陷腔相比,耦合腔阵列结构的缺陷腔模透射率提高三个量级以上,而群速度降低一个量级,得到0.007c的结果.该慢波效应在构造微型可调谐光延迟器和低阈值光子晶体激光器等方面具有潜在的应用前景. 关键词： 光子晶体 耦合腔阵列 慢波 透射率     

一维光子晶体中多缺陷耦合导致的杂质带

利用传输矩阵方法研究了包含多个周期性分布的缺陷的一维光子晶体的透射谱.以33个周期的1/4波堆存在5个缺陷的光子晶体为例作了数值计算.结果表明,在周期性光子晶体中加入多个缺陷时,将在截止带中产生多个缺陷模.这些缺陷模构成的杂质能带依赖于缺陷在晶体中的分布.当缺陷密集时,缺陷模耦合较强,杂质带中透射峰相距较远,它们对应禁带中许多分立定域的杂质能级;当缺陷稀疏时,缺陷模耦合较弱,透射峰相距较近,分立的杂质能级趋于简并,由此形成一个很窄的通带.     

二维光子晶体耦合腔阵列的慢波效应研究

设计了一种六角晶格二维光子晶体耦合腔阵列，平面波展开法计算能带表明，处于禁带中的耦合缺陷腔模的色散曲线在光子晶体平面内所有k矢量方向更加平坦.模拟了横电波沿ΓK方向的透射谱.与光子晶体单缺陷腔相比，耦合腔阵列结构的缺陷腔模透射率提高三个量级以上，而群速度降低一个量级，得到0.007c的结果.该慢波效应在构造微型可调谐光延迟器和低阈值光子晶体激光器等方面具有潜在的应用前景.     

光子晶体波导慢光特性研究

基于二维三角晶格空气孔光子晶体,通过在光子晶体单线缺陷波导两侧引入不同的耦合腔,设计了慢光特性较好的波导结构.利用平面波展开法计算波导的色散曲线,并分析慢光模式的群速度和群速度色散特性.耦合腔采用单缺陷腔时,适当调节波导宽度可以获得在零色散点群速度为0.0128c的慢光模式,对应在1.55 μm波长处的带宽为409 G...     

含具有双增益线原子的光子晶体中的光传播

讨论了缺陷层包含具有双增益线的原子的一维光子晶体中的色散效应及透射谱，双增益线间出现了反常色散区，由于入射光与双增益线的相互作用使得光子带隙中出现了两个透射率远大于1的透射峰；透射峰随着缺陷位置和体系结构参数的变化而产生变化；左透射峰和右透射峰很窄的频率范围内分别出现了斜率极大的反常色散和正常色散，产生了负的群速度和极慢光速的光传播行为。     

反常色散材料光子晶体中光输运的光学控制

研究了光抽运对由铯原子蒸气构成的光子晶体的影响.研究发现,利用较弱光强的线抽运光即可显著地改变这种反常色散光子晶体的透射率.而利用圆偏振光抽运可以进一步降低抽运光的阈值,并在反常色散光子晶体中获得极大的法拉第旋转.反常色散光子晶体的这些特性为光控光开关的研究和制作提供了一条新途径.     

含色散介质的一维光子晶体微腔中简正耦合模的物理图像

对一维光子晶体中的色散介质采用洛伦兹振子模型,对线性层及色散δ层均采用传输矩阵的方法,研究了一维含色散介质的光子晶体微腔中的简正耦合模.通过改变洛伦兹振子和微腔之间的失谐频率,分析了简正耦合模频率的变化情况.在失谐频率比较大时,光与洛仑兹振子间的耦合作用较小,简正耦合模中的一个接近腔模频率,而另一个则接近洛仑兹振子的共振频率;在失谐频率比较小时,光与洛仑兹振子间的耦合作用较大,简正耦合模与未耦合的腔模频率和洛仑兹振子的共振频率之间的差别较为明显.最后通过引进该结构的复有效折射率,对含色散介质的系统,由于带隙中间的共振模被湮灭并分裂为左右两个耦合模,其复有效折射率虚部在原共振峰处跃变为一较大值,而在新生成的两个耦合模附近趋近于零,光与色散介质相互耦合而形成的腔极化激元的物理图像十分清晰.     

含负折射率缺陷的一维光子晶体的杂质带

利用传输矩阵方法研究了含负折射率缺陷的一维光子晶体的透射谱.以19个周期的1/4波堆存在3个负折射率缺陷的光子晶体为例进行了数值计算.结果表明:如果改变缺陷的折射率,缺陷模之间的耦合作用将发生改变,带隙中形成的杂质带也随之改变; 当这个折射率取适当值时,在禁带中出现多个尖锐的透射峰,与正折射率缺陷构成的杂质带不同.     

含负折射率缺陷的一维光子晶体的杂质带

利用传输矩阵方法研究了含负折射率缺陷的一维光子晶体的透射谱.以19个周期的1/4波堆存在3个负折射率缺陷的光子晶体为例进行了数值计算.结果表明:如果改变缺陷的折射率,缺陷模之间的耦合作用将发生改变,带隙中形成的杂质带也随之改变; 当这个折射率取适当值时,在禁带中出现多个尖锐的透射峰,与正折射率缺陷构成的杂质带不同.     

硼氮掺杂对立方PbTiO3电子结构和光学性质影响的第一性原理研究

钛酸铅(PTO)因具有优异的铁电、压电特性及光学性质而备受关注.但B、N掺杂对顺电相PTO电子结构和光学性质的影响还不明确,因此,利用第一性原理对立方PTO开展准确的性质预测尤为必要.本文采用广义梯度近似的PBE泛函(GGA-PBE)和杂化泛函(HSE06)研究了B、N替位掺杂(B_O、N_O)和O空位(V_O)对PTO的基态性质、电子结构和光学性质的影响.研究表明：贫氧态的PTO比富氧态更容易形成杂质缺陷,且N_O缺陷最难形成.当B_O、N_O缺陷存在时,PTO的价带顶和导带底向低能量方向移动,在两者之间出现杂质能级,使其导电性能提高且含B_O的PTO为间接带隙半导体,而含N_O的PTO为直接带隙半导体. N_O体系在波长大约为230 nm处有最大吸收峰,该峰主要源于O 2p和Ti 3d之间的电子跃迁,且N_O体系对可见光的吸收能力最强,有望提高PTO的光催化能力.     

中心外缺陷对带隙型光子晶体光纤色散特性的影响

利用时域有限差分法(FDTD)模拟仿真了在中心缺陷外出现点缺陷、空气柱位错和内层空气柱发生形变三种缺陷形态对光子带隙型光子晶体光纤(PBG-PCF)色散特性的影响.发现一方面缺陷的出现会使色散曲线趋于平坦,另一方面点缺陷和位错缺陷的出现会使零色散点向长波移动,内层空气柱的形变使零色散点向短波长移动.这对PBG-PCF的实际生产实践会有指导意义. 关键词： 带隙型光子晶体光纤 时域有限差分法 缺陷态 色散     

Effect of point defects on electronic and magnetic properties of single-layer SiO

Based on spin-polarised density functional theory calculations, we investigated the effect of point defects on electronic and magnetic properties of the single-layer (SL) asymmetric washboard silicon oxide (aw-SiO). The SL-aw-SiO is a counterpart of black phosphorene, and a new candidate of two-dimensional material family. This structure is dynamically and thermally stable and is a nonmagnetic semiconductor with a direct band gap. We found that single vacancy and divacancy give rise to significant change in the electronic and magnetic properties of SL-aw-SiO. The band gap of aw-SiO can be tuned by the substitution of Si atom instead of O atom, the antisite defect, the O atom vacancy and two atom vacancies. In addition, impurity states due to the defects can occur in the band continua and hence the band gap of aw-SiO is reduced. Having an integer magnetic moment, SL-aw-SiO upon Si vacancy and by substitution of O atom instead of Si atom may display half-metallic features.     

Non-stoichiometry and properties of ternary semiconductor phases of variable composition based on IV-VI compounds

An overview and analysis of our experimental data on the crystal structure, mechanical, thermal, galvanomagnetic and thermoelectric properties vs composition of the ternary semiconductor phases based on IV-Te compounds in the IV-X-Te systems (IV-Ge, Sn, Pb; X-Cu, Ag, Cd, In, Ga, Bi, Sb, Mn, V) are given. The separate and joint effect of deviation from stoichiometry and cation substitution on the IV-X-Te phase properties is established using the method of ‘controlled atomic defects’. Some general regularities and new physical phenomena connected with simultaneous presence of intrinsic and impurity point defects are detected. The influence of the cation substitution on the intrinsic defect equilibrium is established. It is shown that critical phenomena of percolation nature are observed in the range of small impurity contents as well as small intrinsic defect concentrations. Principally new models of the energy band structure of IV-X-Te ternary phases, which take into consideration a high concentration of non-stoichiometric defects, are proposed. The role of long- and short-range ordering is discussed. The formation of complexes as a result of chemical interaction between impurity and host atoms is detected. The above-mentioned phenomena are common for ternary phases and should be taken into account when developing materials for different applications.     

The Formation of Defect Complexes in a ZnO Grain Boundary

The microscopic properties a ZnO grain boundary containing extrinsic point defects are studied using a density functional computational approach. The results show that the grain boundary acts as a sink for native defects, such as the zinc vacancy and the oxygen interstitial, and also for bismuth substitutional impurities. The defects tend to accumulate at under-coordinated sites in the boundary core and prefer to form small clusters. In particular the segregation of Bi promotes the formation of the other native defects by lowering their formation energies in the boundary. Individually, the native defects and the Bi impurity do not produce deep interface states in the band gap which are electrically active. However, when the defects cluster to form a Bi_Zn-V_Zn-O_i complex, new gap states are created of acceptor type. It is suggested that these new states are caused by defect interactions which compensate one another resulting in the depletion of an occupied impurity state and new bond formation. The results are discussed in terms of the Schottky barrier model commonly used to describe the electrical characteristics of ZnO varistors.     

Fe-N共掺杂锐钛矿相TiO2电子性质与光学性质的第一性原理研究

近年来,Fe和N掺杂锐钛矿相TiO2半导体在实验中发现许多优异性能,本文采用基于密度泛函理论的平面波超软赝势方法研究了纯锐钛矿相TiO2、Fe和N单掺杂及Fe和N共掺杂TiO2的能带结构、电荷布居、态密度和光学性质.分析发现:Fe掺杂引起杂质能带位于禁带中央,杂质能带最高点与导带相距大约0.6 eV而最低点与价带相距大约0.2 eV;N掺杂引起的杂质能带位于价带顶部附近. Fe和N共掺杂后杂质能带由两部分组成,位于价带顶上方0.62 eV和导带底下方0.22 eV处,其中一层杂质能带主要由N原子的2p轨道和Fe原子的3d轨道杂化形成,而另一条杂质能带主要由Fe原子的3d轨道形成,由于杂质能级的出现,使锐钛矿TiO2的禁带宽度变小.对光学性质分析发现:Fe和N共掺杂会使锐钛矿TiO2光学吸收带边红移,可见光区的光吸收系数明显增大,在低能区出现了新的吸收峰,对应能量为1.82 eV,与实验结果相符.     

Investigation of the kinetic characteristics of heavily doped compensated CdSnAs2(Cu)

The concentrational dependences of the Hall coefficient and of the resistivity were used to investigate the interaction of diffusively introduced copper impurity with an ensemble of intrinsic defects inn-CdSnAs ₂. The initial electron density and the concentrations of theV _As andCu _As defects were found to be of the same order. A study was made of the dependence of the electrophysical properties ofCdSnAs ₂ (Cu) on the population of the impurity band and it was shown that the features of the kinetic characteristics ofCdSnAs ₂ (Cu) are determined by the absence of an energy gap between the bands with a conductivity of opposite sign and by the fact that one of the bands is an impurity band. State Pedagogical University, Nizhegorod. Kh. I. Amirkhanov Physics Institute, Dagestan Scientific Center, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 62–66, May, 1997.     

Mutual influence of uniaxial tensile strain and point defect pattern on electronic states in graphene

The study deals with electronic properties of uniaxially stressed mono- and multi-layer graphene sheets with various kinds of imperfection: point defects modelled as resonant (neutral) adsorbed atoms or molecules, vacancies, charged impurities, and local distortions. The presence of randomly distributed defects in a strained graphene counteract the band-gap opening and even can suppress the gap occurs when they are absent. However, impurity ordering contributes to the band gap appearance and thereby re-opens the gap being suppressed by random dopants in graphene stretched along zigzag-edge direction. The band gap is found to be non-monotonic with strain in case of mutual action of defect ordering and zigzag deformation. Herewith, the minimal tensile strain required for the band-gap opening (≈12.5%) is smaller than that for defect-free graphene (≈23%), and band gap energy reaches the value predicted for maximal nondestructive strains in the pristine graphene. Effective manipulating the band gap in graphene requires balanced content of ordered dopants: their concentration should be sufficient for a significant sublattice asymmetry effect, but not so much that they may suppress the band gap or transform it into the “quasi- (or pseudo-) gap”.