Na掺杂反式聚乙炔中的孤子晶格的能谱与电子束缚态

从离散的ＳＳＨ模型出发，考虑了链内的电子相互作用，以及由杂质和周围链上的荷电孤子产生的库仑势的影响，探讨了各种掺杂浓度的反式聚乙炔中孤子晶格的能谱与电子束缚态。计算结果表明：在孤子晶格的能谱中，在价带底有两条定域能级，在导带顶存在着多个电子束缚态，随掺杂浓度的升高，束缚态的局域性减弱，禁带中的孤子能级形成孤子能带。当掺杂浓度高达１６．６７％时，所有的电子束缚态都消失，转变为扩展态。孤子晶格的禁带宽度随着掺杂浓度的增加而增大，最高占据态与导带底之间的能隙则随之逐渐减小。孤子能带底与价带顶之间的能隙在临界浓度附近有一极大值。还讨论了电子－电子相互作用对孤子晶格能谱的影响。 关键词：     

掺杂聚乙炔中的边界效应与孤子对稳定性

在自然边界条件下,研究了含有两个杂质离子的反式聚乙炔链中孤子对的稳定性和电子能级结构。所用哈密顿量在SSH模型基础上,附加了一个端点势,并包含了杂质的屏蔽库仑势及格点上e-e相互作用。计算结果显示,杂质离子的库仑作用力程足够长时,链中形成稳定的孤子对,链端的影响增强这种稳定性。带隙宽度随链的增长而变窄,但孤子能级至导带底的跃迁能量随链长变化不明显。 关键词：     

Nitrogen- and fluorine-doped ZrO2: a promising p-n junction for an ultraviolet light-emitting diode

In this work we study the effect of nitrogen (N) and fluorine (F) doping on the electronic properties of ZrO(2) by using ab initio electronic structure calculations. Our calculations show the importance of on-site Coulomb correlation in estimating the correct band gap of ZrO(2). The N and F doping provide hole- and electron-type impurity states in the band gap closer to the top of the valence band and the bottom of the conduction band, respectively. The formation of such impurity states may be exploited in fabricating a p-n junction expected to be useful in making an ultraviolet light-emitting diode.     

Numerical simulation of the temperature dependence of the ionization energy of hydrogen-like impurities in semiconductors: Application to transmutation-doped Ge: Ga

An electrostatic model describing the dependence of the thermal ionization energy of impurities on their concentration, compensation factor, and temperature is developed. The model takes into account the screening of impurity ions by holes (electrons) hopping from impurity to impurity, the change in the impurity-band width, and its displacement with respect to the edge of the valence band for acceptors (conduction band for donors). The displacement of the impurity band is due to the functional dependence of the hole (electron) affinity of the ionized acceptor (donor) on the screening of the Coulomb field of the ions. The spatial distribution of the impurity ions over the crystal was assumed to be Poisson-like, and the energy distribution was assumed to be normal (Gaussian). For the relatively low doping levels under investigation, the behavior of the density of states at the edges of the valence and conduction bands was assumed to be the same as for the undoped crystal. The results of the numerical study are in agreement with the decrease in the ionization energy that is experimentally observed for moderately compensated Ge: Ga as the temperature and the doping level are decreased. It is predicted that the temperature dependence of the thermal ionization energy has a small anomalous maximum at small compensation factors.     

稀土元素Lu，Sc掺杂GaN光电特性的第一性原理研究

基于密度泛函理论,采用广义梯度近似（GGA+U）平面波超软赝势方法,计算了本征GaN和稀土元素Lu、Sc掺杂GaN体系的电子结构和光学性质.结果表明：计算得到本征GaN的禁带宽度为3.37 eV,与实验值（3.39 eV）接近. Lu掺杂后GaN体系带隙变窄,而Sc掺杂后诱导了深能级杂质,带隙变宽,但仍为直接带隙半导体.掺杂后体系均发生畸变,晶格常数和体积增大,且在费米能级附近产生杂质带. Lu、Sc掺杂GaN体系的静态介电常数较本征GaN（4.50）均有所增大.Lu、Sc掺杂后体系介电常数虚部整体左移,光吸收边往低能方向移动,发生了红移现象.计算结果对稀土元素Lu、Sc掺杂GaN高压光电材料的开发和研究提供了理论依据.     

Features of the fine structure of the fundamental absorption edge in low-doped semiconductor quantum wells with allowance for the Coulomb gap

Influence of the Coulomb gap on the fine structure of the fundamental absorption edge in quantum wells is studied. Using the interpolation formula, which adequately describes the effect of the Coulomb gap in quantum wells under conditions of low doping regardless of the compensation degree, an explicit expression is obtained for the absorption coefficient related to transitions from the valence level of size quantization to the impurity band. The dependence of the absorption coefficient of a quantum well on the levels of doping and compensation is also studied.     

Influence of oxygen impurities on the electronic properties of graphene nanoflakes

Controlled chemical doping with oxygen impurities is a promising approach for the electronic band engineering of graphene nanoflakes (GNFs). Based on the first-principles of the density functional theory (DFT) calculations, we investigated the effect of various consternations of substitutional impurities from oxygen atoms on the electronic properties of GNFs. Our results show that the electronic properties of GNFs do not only depend on the oxygen impurity concentrations, but also depend on the geometrical pattern of oxygen impurities in the GNFs. Additionally, we also found interesting electronic properties of GNFs structure, which significantly contribute to that oxygen dopants cause a decreased energy gap. So, our results suggest that substitutional impurities are the best viable option for enhancement of desired electronic properties of GNFs.     

Radiotracer spectroscopy of deep levels in the semiconductor band gap

Basic electronic properties of semiconductors are determined by defects and impurities. Extremely small relative concentrations may have an effect, if the impurity in question gives rise to a localized electron state having an energy within the band gap of the semiconductor. Among the techniques available to characterize band gap states, the present paper focuses on Deep Level Transient Spectroscopy (DLTS). To derive a definite chemical identification of the band gap states detected, radioactive isotopes are used as a tracer. Characteristic concentration changes of band gap states (detected by repeated DLTS measurements during the elemental transmutation) clearly reveal the involvement of a radioisotope in the formation of a certain defect level. The key issues of a radiotracer experiment are the radioactive doping process and the interpretation of transmutation-induced phenomena. Critical aspects are illustrated on the basis of recent radiotracer-DLTS studies in the semiconductors silicon and silicon carbide. This revised version was published online in August 2006 with corrections to the Cover Date.     

共轭高聚物中的杂质分布:晶格形态及高浓度掺杂效应

基于扩展Su-Shrieffer-Heeger(SSH)模型,通过自洽计算的数值方法,研究了共轭高聚物链表现为孤子态和大极化子态两种不同晶格形态时链内的杂质分布情况,计算结果显示,分立的畴壁可导致高聚物链中形成多个稳定的势阱,有利于杂质在链中聚集分布.此外,还研究了在较高浓度的掺杂条件下,共轭高聚物链内的杂质分布规律.结果显示,杂质倾向于在中心区形成高浓度分布,而在链端区,杂质更倾向于离散分布.该研究表明,高浓度掺杂下杂质分布具有稳定的特征,晶格形态对杂质分布具有显著的影响,这些结论可为实验上操控杂质在共轭高聚物中的分布提供一定的帮助.     

共轭高聚物中的杂质分布：晶格形态及高浓度掺杂效应

基于扩展Su-Shrieffer-Heeger (SSH)模型,通过自洽计算的数值方法,研究了共轭高聚物链表现为孤子态和大极化子态两种不同晶格形态时链内的杂质分布情况,计算结果显示,分立的畴壁可导致高聚物链中形成多个稳定的势阱,有利于杂质在链中聚集分布。此外,还研究了在较高浓度的掺杂条件下,共轭高聚物链内的杂质分布规律。结果显示,杂质倾向于在中心区形成高浓度分布,而在链端区,杂质更倾向于离散分布。该研究表明,高浓度掺杂下杂质分布具有稳定的特征,晶格形态对杂质分布具有显著的影响,这些结论可为实验上操控杂质在共轭高聚物中的分布提供一定的帮助。     

Effects of acceptor–donor complexes on electronic structure properties in co-doped TiO2: A first-principles study

We theoretically investigate the doping effects induced by impurity complexes on the electronic structures of anatase TiO₂ based on the density functional theory. Mono-doping and co-doping effects are discussed separately. The results show that the impurity doping can make the band-edges shift. The induced defect levels in the band gaps by impurity doping reduce the band gap predominantly. The compensated acceptor–donor pairs in the co-doped TiO₂ will improve the photoelectrochemical activity. From the calculations, it is also found that (S+Zr)-co-doped TiO₂ has the ideal band gap and band edge, at the same time, the binding energy is higher than other systems, so (S+Zr)-co-doping in TiO₂ is more promise in photoelectrochemical experiments.     

Electronic structure and optical properties of anatase doped with bismuth and carbon

The calculations of the electronic structure of pure anatase and the anatase doped with carbon and/or bismuth have been carried out using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) method in the local spin density approximation with the inclusion of single-site Coulomb correlations (LSDA + U). The dielectric function, absorption coefficient, and refractive index have been calculated in the random phase approximation. It has been found that, upon doping, narrow bands of carbon and bismuth impurity states are formed in the band gap. The calculations of the optical absorption coefficient have demonstrated that the C,Bi-doping can lead to the absorption in the visible region and an enhancement of the absorption in the near-ultraviolet region. Therefore, the C,Bi-doping can increase the photocatalytic activity on the surface of doped anatase.     

Mn掺杂6H-SiC的第一性原理研究

本文通过密度泛函理论第一性原理平面波超软赝势计算方法计算了Mn掺杂6H-SiC的电子结构与光学性质。计算结果显示掺杂Mn后的6H-SiC为间接带隙p型半导体,且带隙较本征体有所降低,带隙由2.022 eV降为0.602 eV,电子从价带跃迁所需能量减少。掺杂后的Mn的3d能级在能带结构中以杂质能级出现,提高了载流子浓度,导电性增强。光学性质研究中,掺杂Mn后的介电函数虚部在低能处增加,电子激发态数量增多,跃迁概率增大。掺杂后的光吸收谱能量初值也较未掺杂的3.1 eV扩展到0 eV,反射谱发生红移。由于禁带宽度的降低使得光电导率起始范围得到扩展。     

Electronic states at junctions of molecular semiconductors

We consider properties of junctions for the field effect transistors (FET) geometry where molecular crystals or conducting polymers are used as semiconducting layers. In the molecular crystal Coulomb interaction of free electrons with surface polar phonons of the dielectric layer can lead to self-trapping of carriers and to the formation of a strongly coupled long-range surface polaron. The effect is further enhanced in presence of the bias electric field and strongly depends on the gate dielectric used.In conducting polymers instead of the usual band bending near the contact interface, new allowed electronic bands appear inside the band gap. As a result the bias electric field and the injected charge penetrate into the polymer via creation of the soliton lattice whose period changes with the distance from the contact surface. The current through the contact is performed via moving solitons.     

Dynamical Stability of Gap Soliton of One-Dimensional Condensate in Optical Lattices with Strong Interatomic Interaction

By developing the multiple scales method, we analytically study the dynamics properties of gap soliton of Bose- Einstein condensate in optical lattices. It is shown that the gap soliton will appear at Brillouin zone edge of linear band spectrum of the condensates when the interatomic interaction strength is larger than the lattice depth. Moreover, the density of gap soliton starts to be relatively small, while it increases with time and becomes stable.     

Doping in silicon nanocrystals: An ab initio study of the structural, electronic and optical properties

There are experimental evidences that doping control at the nanoscale can significantly modify the optical properties with respect to the pure systems. This is the case of silicon nanocrystals (Si-nc), for which it has been shown that the photoluminescence (PL) peak can be tuned also below the bulk Si band gap by properly controlling the impurities, for example by boron (B) and phosphorus (P) codoping. In this work, we report on an ab initio study of impurity states in Si-nc. We consider B and P substitutional impurities for Si-nc with a diameter up to 2.2 nm. Formation energies (FEs), electronic, optical and structural properties have been determined as a function of the cluster dimension. For both B-doped and P-doped Si-nc the FE increases on decreasing the dimension, showing that the substitutional doping gets progressively more difficult for the smaller nanocrystals. Moreover, subsurface impurity positions result to be the most stable ones. The codoping reduces the FE strongly favoring this process with respect to the simple n-doping or p-doping. Such an effect can be attributed to charge compensation between the donor and the acceptor atoms. Moreover, smaller structural deformations, with respect to n-doped and p-doped cases, localized only around the impurity sites are observed. The band gap and the optical threshold are largely reduced with respect to the undoped Si-nc showing the possibility of an impurity-based engineering of the Si-nc PL properties.     

Electronic properties of BN-doped bilayer graphene and graphyne in the presence of electric field

In the present paper, we have used density functional theory to study electronic properties of bilayer graphene and graphyne doped with B and N impurities in the presence of electric field. It has been demonstrated that a band gap is opened in the band structures of the bilayer graphene and graphyne by B and N doping. We have also investigated influence of electric field on the electronic properties of BN-doped bilayer graphene and graphyne. It is found that the band gaps induced by B and N impurities are increased by applying electric field. Our results reveal that doping with B and N, and applying electric field are an effective method to open and control a band gap which is useful to design carbon-based next-generation electronic devices.     

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.     

Artificial carrier heating due to the introduction of ab initio Coulomb scattering in Monte Carlo simulations

Accurately treating ionised impurity scattering in a way suitable to describe the influence of random dopant fluctuations on device characteristics is important in next generation MOSFETs. Statistical variations are unobservable using a continuous treatment of the doping, requiring a discrete representation of impurities. In particle-based simulations the P³M method, which resolves the Coulomb interaction into long- and short-range components, is in principle capable of describing Coulomb scattering through propagation in this accurately resolved potential. However, numerically the integration of the equations of motion is inaccurate and controlling the errors in practical simulations is vital. In this paper we investigate the effect of the choice of short-range correction strategy and integration time step on accuracy in a 3D self-consistent ensemble Monte Carlo simulations featuring random discrete dopants. We illustrate the importance of the ‘ab initio’ Coulomb scattering comparing the effect of a single trapped charge in drift-diffusion and Monte Carlo simulations.     

High UV absorption efficiency of nanocrystalline ZnO synthesized by ultrasound assisted wet chemical method

Ultrasound assisted wet-chemical method has been carried out to incorporate different metal and non-metal ions such as; Li, S and Ag into ZnO. Characteristic studies on the structural and optical properties of the samples especially; the ultra-violet (UV) light absorption have been carried out. X-ray diffraction (XRD) analysis shows the formation of hexagonal crystal structure of ZnO along with changes in crystallinity and micro-strain with impurity doping. The morphology of the doped samples changes from particle like structure to flower and rod like structures showing the influence of dopant ions on nano ZnO growth. Infra-red (IR) transmittance spectra give information about the presence of metal–oxygen bond along with other stretching and bending modes. UV–visible absorption studies show the narrowing and sharpening of UV absorption band along with a blue shift for the doped samples. This shows the intensification in the excitonic absorption in ZnO after doping specific elements which will find application in UV blocking agents. Photoluminescence (PL) measurement shows the presence of excitonic emission and emissions due to intrinsic defects and external impurities in UV and visible regions respectively. These emission bands show a change in their position and intensity which has been explained on the basis of the existence of impurity levels in the band gap of ZnO.