On the evaluation of the dopant concentration of a three-dimensional steady-state constant-source diffusion problem

In this paper, we consider a three-dimensional steady-state constant-source diffusion problem. On the surface of a half space, the dopant concentration function is prescribed over a circular area and its normal derivative is zero over the remaining part of the boundary. The analytical solution of this problem has been known for over half a century. Due to the complexity of the solution, it seems that nobody has ever used it on the direct evaluation of the dopant concentration in the half space. This paper shows that, to be able to evaluate directly, the prescribed boundary function has to be expressed by a power series. It may be used as special cases to verify numerical diffusion models, which consider time-evolutions of dopant concentrations and non-constant diffusion coefficients.     

Power losses in deformed graded-index polymer optical fibers

We investigate the power losses in bent and elongated graded-index polymer optical fibers (GI POFs). The variations of power losses in deformed GI POFs for various radii of curvature and elongations are measured. A simple tensile test result is used to calculate the average plastic energy density (APED) in a deformed GI POF at various elongations. The results indicate that the APED accumulated in a deformed GI POF can be considered as a key index to study the power loss in POF. Based on the experimental results, a curve-fitted equation is proposed to estimate the power loss using the APED for various radii of curvature. The maximum difference between the proposed equation and the experimental results is less than 3% for the deformed GI POFs.     

Influence of initial dopant distribution in fiber core on refractive index distribution of thermally expanded core fibers

We investigate the process of dopant diffusion of a thermally expanded core fiber by solving the corresponding diffusion equation using the explicit finite-difference method. We compare our numerical solution with analytical solution of diffusion equation for two different initial dopant concentrations in the core. The conclusions reached provide a guideline for the accurate modeling of dopant diffusion of thermally expanded core fibers, which is important for the prediction of the mode field enlargement.     

150m聚合物光纤125Mbps传输实验

根据阶跃型聚合物光纤的耦合长度分析了模式耦合对其带宽的影响,结果表明,由于聚合物光纤中存在较强的模式耦合,其传输带宽不是与传输距离成反比而是与传输距离的平方根成反比,从而其带宽得到了很大的提高。在此基础上,使用商用阶跃型聚合物光纤成功地进行了125Mbps·150m的局域网传输实验,对比了系统的发射和接收信号,得到了较好的通信眼图。实验结果显示,聚合物光纤完全可以进行较长距离的高速数据传输,改变了一般认为的聚合物光纤百兆速率传输距离在100m以内的状况。     

Theoretical analysis on the refractive-index distribution and bandwidth of gradient-index polymer optical fibers from a centrifugal field

Theoretical analysis was applied to analyze the refractive-index distribution (RID) and bandwidth (BW) of gradient-index polymer optical fibers (GI POFs) prepared by a centrifugal field process. The RID of the prepared GI POF could be represented by the equation of n(r) = n1[1 - 2delta(r/alpha)g](1/2). The studied material systems were poly(hexafluoroisopropyl 2-fluoroacrylate) (PHFIP 2-FA)/dibutyl phthalate (DBP) and poly(methyl methacrylate) (PMMA)/benzyl benzoate (BEN). The RID and the BW were significantly affected by an essential parameter k, which was related to thematerial properties (density difference and molecular weight) and processing properties (rotating speed, temperature, and radius). As k increased, the characteristic constant of RID, g, decreased to a minimum and then increased sharply, owing to the separation of the polymer and the dopant. On the other hand, the relative refractive-index difference of RID, delta, increased to a steady value after k increased to a certain value. The variation of RID with k resulted in a local minimum of intermodal dispersion, and thus a maximum bandwidth was obtained. The maximum BW of the PHFIP 2-FA/DBP and PMMA/BEN systems at 1550 nm (100-m fiber length and 2-nm spectral width) for the case of k not equal to 0 were 6.7 and 3.2 Gb/s, respectively. The wavelength of light source affects the BW significantly only at k around zero because of the importance of the intramodal dispersion in this case.     

The application of the loop annealing technique to self diffusion studies in silicon

The loop annealing technique has been applied to the study of self diffusion in silicon over a wide range of doping concentrations. The results show that the diffusion coefficient decreases as the concentration of n-type dopant decreases and the concentration of p-type dopant increases. At a fixed temperature, the diffusion coefficient is linearly dependent on the electron concentration and this behaviour is in accord with the point defects responsible for self diffusion behaving as acceptors. The values obtained for the self diffusion coefficient in intrinsic material are in good agreement with those obtained by other workers at higher temperatures using profiling techniques and indicate a slight curvature in the Arrhenius plot.     

Synthesis and characterization of bismuth doped barium sulphide nanoparticles

We have synthesized BaS:Bi nanocrystalline powder of average grain size 35 nm by solid-state diffusion method using sodium thiosulphate as a flux. During this work we have optimized the nature and amount of flux, amount of the dopant and temperature of firing for maximum yield of photoluminescence. The samples were characterized by X-ray powder diffraction (XRD) method, transmission electron microscopy (TEM), photoluminescence (PL) and UV-visible techniques. On excitation by 425 nm, these nanophosphors give one emission peak at 575 nm which corresponds to green color. In the excitation spectra of these particles there are two peaks at 350 nm and 425 nm. The effect of dopant concentration on the photoluminescence of BaS:Bi nanocrystallites has been studied which is in agreement with the principle of concentration quenching. The energy band gap of bismuth doped BaS nanopowder has been calculated to be 4.25 eV and is blue shifted in comparison to their bulk counterparts. The blue shift may be due to the quantum confinement in the particles.     

聚合物熔体复合挤出胀大过程的数值模拟及可恢复弹性形变分析

建立了两种聚合物熔体流经矩形流道共挤出的三维数值计算模型,采用有限元方法数值模拟了共挤出成型过程及胀大过程,得到了速度场、压力场、应力场,并利用数值计算方法得到了共挤出流动过程的可恢复弹性形变场,分析了挤出胀大率以及可恢复弹性形变的变化过程。结果表明,在共挤出流动的胀大段,共挤出界面的形状和位置发生了改变;经矩形流道共挤出得到的挤出胀大末端截面形状为不对称的鼓形;在共挤出界面附近可恢复弹性形变值存在极值,运用数值方法计算可恢复弹性形变可以对流动过程中可能存在的缺陷进行预测。     

Field mapping with nanometer-scale resolution for the next generation of electronic devices

In order to improve the performance of today's nanoscaled semiconductor devices, characterization techniques that can provide information about the position and activity of dopant atoms and the strain fields are essential. Here we demonstrate that by using a modern transmission electron microscope it is possible to apply multiple techniques to advanced materials systems in order to provide information about the structure, fields, and composition with nanometer-scale resolution. Off-axis electron holography has been used to map the active dopant potentials in state-of-the-art semiconductor devices with 1 nm resolution. These dopant maps have been compared to electron energy loss spectroscopy maps that show the positions of the dopant atoms. The strain fields in the devices have been measured by both dark field electron holography and nanobeam electron diffraction.     

Thallium and indium doped Pb1−xSnxTe by liquid phase epitaxy

Doped Pb_1?xSn_xTe epilayers have been grown on PbTe substrates by liquid phase epitaxy using lead-rich melts containing thallium or indium. Thallium is a p-type dopant; indium is an n-type dopant. It is also demonstrated that the doped layers can be annealed under conditions that convert undoped material from n to p-type, or vice-versa, without themselves being converted. This is the first application of doping to lead-tin salt LPE and significantly increases the flexibility of this technique for fabricating detector and laser heterostructures.     

Electron energy-loss spectroscopy investigation of dopant homogeneity in Tb-doped Y2O3 nanoparticles prepared by solution combustion synthesis

The emergence of nanotechnology imposes a new level of control in the synthesis of materials, one in which the structure and chemistry have to be controlled and characterized at the nanoscale. The solution combustion synthesis method has been used to synthesize many different oxides, including luminescent ones. However, a systematic investigation of the dopant homogeneity at the nanoscale in materials produced by this method is lacking. This is of particular relevance in nanophosphors due to the possibility of concentration quenching. In this work, 5 at.% Tb-doped Y₂O₃ was prepared by the solution combustion synthesis method and investigated on its structure and chemical composition homogeneity at the nanoscale by means of electron energy-loss spectroscopy (EELS) scanning transmission electron microscopy (STEM), high resolution TEM, X-ray diffraction and photoluminescence measurements. The results show that it is possible to prepare luminescent materials by the solution combustion synthesis method where the dopant is homogeneously distributed within each nanoparticle.     

Radial junctions formed by conformal chemical doping for innovative hole-based solar cells

In this paper an innovative approach for Si solar cells based on radial junctions is presented. It consists of fabricating the junction in quasi one-dimensional structures like holes. The hole-based architecture, while maintaining the decoupling between the light absorption and the electrical collection typical of the more common wires and rods, ensures more robustness, numerous waveguide coupling modes and possibility to form non-conformal top contact. Nanosizes also provide the possibility to tune the band gap by quantum effects. Doping of the nanoholes, like in the case of nanowires, presents critical issues like conformality and control of the dopant dose and junction depth at nanometric level. We propose to dope the nanoholes by using a chemical method based on the use of a dopant containing molecules dispersed in solution. We apply the procedure on an array of holes of micrometric sizes fabricated to test and study the method and to properly scale it down and implement it on the nanostructures. Results show that the method provides junction depths in the nm scale with dopant peak concentrations as high as 10¹⁹ cm^?3 and that the doping is conformal on the vertical surfaces of the hole.     

聚合物光纤网络器件及其通信链路系统

通过自行研制的聚合物光纤波长转换器和集线器,实现了石英光纤传输介质到聚合物光纤传输介质的工作波长转换,以及多路聚合物光纤传输信息的交换和局域网信息的全聚合物光纤传输。系统测试结果显示,数据交换传输速率达到100Mbps,通信眼图清晰。链路系统传输信号随传输距离成指数衰减,与聚合物光纤的光强衰减规律一致。用商用的发射接收器测得传输距离达到60m以上。聚合物光纤弯曲半径为25mm时,给系统接收端接收信号强度带来0.1~0.4dB的衰减,表明聚合物光纤弯曲对链路系统工作影响较小。     

A reliable method for the counting and control of single ions for single-dopant controlled devices

By 2016, transistor device size will be just 10?nm. However, a transistor that is doped at a typical concentration of 10(18)?atoms?cm(-3) has only one dopant atom in the active channel region. Therefore, it can be predicted that conventional doping methods such as ion implantation and thermal diffusion will not be available ten years from now. We have been developing a single-ion implantation (SII) method that enables us to implant dopant ions one-by-one into semiconductors until the desired number is reached. Here we report a simple but reliable method to control the number of single-dopant atoms by detecting the change in drain current induced by single-ion implantation. The drain current decreases in a stepwise fashion as a result of the clusters of displaced Si atoms created by every single-ion incidence. This result indicates that the single-ion detection method we have developed is capable of detecting single-ion incidence with 100% efficiency. Our method potentially could pave the way to future single-atom devices, including a solid-state quantum computer.     

Impurity-induced disordering in III–V multi-quantum wells and superlattices

Impurity-induced disordering seems to be a general phenomenon affecting all III–V materials. This paper reviews this phenomenon. Before the available data on impurity-induced disordering is discussed, the diffusion mechanisms for the dopants are briefly reviewed, and for silicon-doped material a more detailed discussion is provided because of its technological importance. Moreover, there has been no critical review of the recent progress in silicon diffusion mechanisms. In zinc-diffused multi-quantum wells and superlattices the mechanism for the enhancement of the interdiffusion seems to be primarily by the fast diffusion of group III interstitials whose concentration has been significantly increased over their equilibrium value by the diffusion of the dopant. For silicon impurity-induced disorder the situation is less clear. However, it is certain that the effect of the position of the Fermi level on the native defect concentrations plays a significant role in the disordering mechanism. The study of the other dopants which cause diffusion-induced disordering is less advanced. For n-type dopants there is an argument which suggests that they all have a common cause, namely the increase in the group III triply charged vacancy which is caused by the increase in the Fermi energy. This will be explored in this review. A brief discussion of ion implantation-induced disordering is also provided. This essentially provides a bibliography of the past work in this field. It is clear, for at least one dopant, that there needs to be some damage to the crystal before the enhancement of the interdiffusion occurs. However, for other dopants too much damage reduces the enhancement of the intermixing.     

Room temperature self-organized gold nanoparticles materials for embedded electronic devices

In this study, we synthesize two different sizes of gold nanoparticles (NPs) with uniform size distribution. A novel technique of fabricating gold NPs embedded capacitor devices utilizing chemical self-assembled gold NPs has been developed. Room temperature process and uniform size distribution of gold NPs device are built and characterized. These electronic devices have lower leakage current, no metal diffusion problem, larger memory window, better charge retention time and following Fowler–Nordheim tunneling model. This method enables the possibility of future memory applications to fabricate devices with this simple and versatile technique based on the NPs assembly.     

Modeling of diffusion and oxidation in two dimensions during silicon device processing

A process simulator named “2D-DIFFUSE” has been developed where the coupled diffusion equation of dopant impurity and point defects: interstitials and vacancies, has been solved numerically in two-dimension. The interaction of point defects has been modeled assuming quasi (i.e. local) equilibrium,C ₁ C _v=C ₁*C*_V and constant vacancy,C _v=C _v*, conditions. Indeed, these two assumptions decouple the two point defects diffusion equations. The processes modeled in the present version of the simulator include pre-deposition, diffusion and oxidation. The simulator is quite successful at modeling each process individually as well as integrating various processes and models. The program has also been applied to the simulation of phenomena as the dopant diffusion under various ambients, oxidation enhanced and retarded diffusion, emitter push effect etc. Comparisons between simulation based on point defect parameters from various sources have been made.     

Lattice Monte Carlo simulations as link between ab-initio calculations and macroscopic behavior of dopants and defects in silicon

In this work, we show that lattice Monte Carlo simulations can be used to span the time and distance scales between underlying atomistic processes and macroscopic diffusion behavior. We use ab- initio calculations of binding energies versus configuration to calculate hopping rates of vacancies for use in lattice Monte Carlo (LMC) simulations of diffusion and aggregation in silicon. The LMC simulations consider the biased nature of vacancy hop frequencies in the neighborhood of dopants, with interactions up to sixth-nearest- neighbor distances included. We use these simulations to investigate the expected macroscopic diffusion behavior, as well as the process by which dopant/defect aggregation occurs. Specific phenomena investigated include collective behavior leading to greatly enhanced diffusivity at high doping levels, the time dependence of effective diffusivity due to the formation of dopant/vacancy clusters, and dopant fluxes in the presence of a vacancy gradient.     

On the FinFET extension implant energy

The need of an ultrashallow junction technology for the extension of p-FinFETs has been investigated by integrated process and device simulations. For devices with 60 nm physical gate length, whose extensions are activated in a low thermal-budget process (spike anneal), it is found that the I/sub off/-I/sub on/ performance is invariant with respect to the extension implant energy. Nevertheless, the short-channel behavior worsens. This can be remedied by adding spacers to both sides of the gate before the extension implant, resulting in virtually identical dc characteristics and speed. Devices with gate lengths of 18 nm and below require dopant activation with negligible diffusion. Under those circumstances the short channel behavior of the FinFET is limited by the lateral straggle of the ion implant. Spacers may remedy what is otherwise poor short channel behavior due to a relatively high energy extension implant. However, this comes at the price of drastically worse drive current at a fixed off-current.     

聚合物气辅共挤成型中挤出胀大的数值模拟

以一矩形截面共挤型材为例,采用Giesekus本构方程和Navier滑移模型建立数值模型,使用EVSS、SU等有限元方法对气辅共挤和传统共挤时两种聚合物熔体在口模内外的等温粘弹流动做了三维数值模拟,得到了气辅共挤和传统共挤时的挤出胀大率、速度场、应力场及剪切速率分布。对模拟结果进行了分析和对比,结果表明,气辅共挤能消除挤出胀大和模外熔体偏转流动现象;气辅共挤时两相熔体的速度场均匀一致,熔体流动稳定,呈柱塞状挤出;熔体表面的切向和法向应力为零,因而可有效提高挤出速率,并防止制品表面"鲨鱼皮"现象的出现。