The QE numerical simulation of PEAsemiconductor photocathode

Several kinds of models have already been proposed to explain the photoemission process. The exact photoemission theory of the semiconductor photocathode was not well established after decades of research. In this paper an integral equation of quantum efficiency (QE) is constructed to describe the photoemission of positive electron affinity (PEA) of the semiconductor photocathode based on the three-step photoemission model. Various factors (e.g., forbidden band gap, electron affinity, photon energy, incident angle, degree of polarization, refractive index, extinction coefficient, initial and final electron energy, relaxation time, external electric field and so on) have an impact on the QE of the PEA semiconductor photocathode, which are entirely expressed in the QE equation. In addition, a simulation code is also programmed to calculate the QE of the K₂CsSb photocathode theoretically at 532 nm wavelength. By and large, the result is in line with the expected experimental value. The reasons leading to the distinction between the experimental and theoretical QE are discussed.     

器件效应数值模拟中漂移扩散模型的误差分析

为了确定数值模拟过程中的误差来源,并针对误差来源改进软件,减小计算误差,对半导体器件数值模拟中的采用的漂移扩散模型进行了研究。结合自主开发的半导体器件效应软件GSRES,分析了软件中漂移扩散模型的理论近似,对计算模型中由于温度分布、载流子复合/产生率、载流子迁移率等项采取近似而导致的误差进行了分析。根据误差分析和数值模拟算例,认为误差主要来自于器件内部温度场分布和迁移率模型的近似,给出了软件的适用范围。结合半导体器件的研究热点和发展趋势,对该模型中需要进行改进的近似项进行了分析。     

器件效应数值模拟中漂移扩散模型的误差分析

为了确定数值模拟过程中的误差来源,并针对误差来源改进软件,减小计算误差,对半导体器件数值模拟中的采用的漂移扩散模型进行了研究。结合自主开发的半导体器件效应软件GSRES,分析了软件中漂移扩散模型的理论近似,对计算模型中由于温度分布、载流子复合/产生率、载流子迁移率等项采取近似而导致的误差进行了分析。根据误差分析和数值模拟算例,认为误差主要来自于器件内部温度场分布和迁移率模型的近似,给出了软件的适用范围。结合半导体器件的研究热点和发展趋势,对该模型中需要进行改进的近似项进行了分析。     

场助InGaAsP/InP异质结半导体光电阴极的研究

本文通过对InGaAsP/InP场助异质结半导体光电阴极的材料生长、场助肖特基结的制备及阴极激活等工艺的系统研究,研制出具有较高光谱响应的半导体光电阴极,生长出优于文献报道的晶格失配率标准的材料,得到相当80年代国际水平理想因子值的场助肖特基结,用实验数据介绍提高量子效率数量级的方法和条件.研究结果表明场助异质半导体光电阴极是在红外波段很有潜力的光电发射体.     

衍射图样的数值模拟

介绍了平面波角谱理论中得到衍射积分公式的方法.用Matlab计算了15×15矩孔阵列近场区域的衍射图样,在距离周期衍射屏特定距离处出现衍射屏的自成像.     

Large-signal simulation of semiconductor lasers on device level: numerical aspects of the harmonic balance method

Large-signal modulation characteristics are key specifications in analog and digital applications of optoelectronic devices. In this work we present a novel approach for the modeling of these characteristics for semiconductor lasers on device level. A multi-tone harmonic balance method for a physics-based electro-thermal-optical model is utilized. The numerical aspects of the framework are described and illustrated for a realistic VCSEL example.     

Thin film semiconductor islands and numerical experiment

The distribution functions of island nuclei of germanium melt drops on Si(100) substrate over lateral sizes and heights in the presence of a surface linear defect are obtained in a numerical experiment simulating the initial stage of the first-order phase transition. A similar model of heterogeneous condensation of silicon carbide vapor is discussed. Quasi-linear kinetic partial differential equations are solved by the efficient numerical method of stochastic analogue of nonequilibrium processes. The Volmer-Weber mechanism of cluster formation from melt islands, their crystallization, and island structure formation on the substrate are considered.     

半导体断路开关数值模拟

 为了研究半导体断路开关(SOS)的截断过程及其在脉冲功率系统中的工作特性,建立了半导体断路开关的电流控制模型,对p⁺-p-n-n⁺掺杂结构的半导体断路开关进行了数值模拟研究。通过数值模拟,给出了p⁺-p-n-n⁺型半导体断路开关在正、反向泵浦过程中的载流子及电场分布,并获得了电流截断效应。计算结果表明,半导体断路开关的截断过程首先发生在p区。     

The optimal thickness of transmission-mode GaN photocathode

A 150-nm-thick GaN photocathode with an Mg doping concentration of 1.6× 10¹⁷cm^-3 is activated by Cs/O in ultrahigh vacuum chamber, and quantum efficiency (QE) curve of negative electron affinity transmission-mode (t-mode) GaN photocathode is obtained. The maximum QE reaches 13.0% at 290 nm. According to the t-mode QE equation solved from the diffusion equation, the QE curve is fitted. From the fitting results, the electron escape probability is 0.32, the back-interface recombination velocity is 5× 10⁴ cm·s^-1, and the electron diffusion length is 116 nm. Based on these parameters, the influence of GaN thickness on t-mode QE is simulated. The simulation shows that the optimal thickness of GaN is 90 nm, which is better than the 150-nm GaN.     

GaN光电阴极激活后的光谱响应分析

由于GaN光电阴极的突出性能,其在紫外探测方面有着广泛的应用.文章在超高真空激活系统中,对GaN样品进行了 Cs/O激活实验,并分析了激活后反射式的量子效率:在240～350nm的紫外波段内,量子效率约在30％～10％之间,曲线较为平坦,在240nm处达到30％的最大值,与国外结果对比后发现,本文获得的GaN光电阴极量...     

The three-dimensional numerical simulation of aluminized composite solid propellant combustion

A three-dimensional numerical framework is presented that examines the burning of aluminized solid propellants. The numerical solver accounts for heat conduction in the solid, combustion in the gas phase, and coupling of these by means of a level set method. The aluminium particles are treated as heat conducting solid spheres. The aluminium particle detachment process is modelled using level sets, but once the particle becomes free from the surface, its subsequent motion in the gas phase is governed by particle dynamics. Some preliminary calculations of the three-dimensional combustion field supported by a pack with embedded aluminium particles are presented.     

基于快速傅里叶变换的衍射现象的数值仿真

根据夫琅禾费衍射与傅里叶变换的关系,通过构建数值遮光屏,并利用快速傅里叶变换,可以获得夫琅禾费衍射图样的二维仿真及其相对光强的三维分布图．利用Matlab实现了对单缝、圆孔及多缝的衍射现象的仿真．结果显示,该方法思路清晰,结果准确可靠,可作为教学中分析夫琅禾费衍射现象的另一种有效方法．     

The numerical simulation of two-dimensional aluminized composite solid propellent combustion

A numerical framework is presented which examines, for the first time, the burning of two-dimensional aluminized solid propellants. Aluminized composite propellants present a difficult mathematical and numerical challenge because of complex physics and topological changes that occur at the propellant surface. For example, both mathematical models and appropriate numerical solvers must describe the regressing burning surface, aluminium particle detachment and evolution throughout the gas-phase flow field, surface tension effects, ignition and combustion of aluminium particles, phase change effects, agglomeration of aluminium particles, radiation feedback to the propellant surface, to name a few. All of these effects must be modelled in a consistent manner. A numerical framework for which these effects can be included in a rational fashion is currently being developed. This framework includes the level set method to capture the solid–gas interface as well as particle motion in the gas phase. Some preliminary calculations of the two-dimensional combustion field supported by a disc pack with embedded aluminium particles are presented.     

The optimal thickness of a transmission-mode GaN photocathode

A 150-nm-thick GaN photocathode with a Mg doping concentration of 1.6×1017cm-3 is activated by Cs/O in an ultrahigh vacuum chamber,and a quantum efficiency(QE) curve of the negative electron affinity transmission-mode(t-mode) of the GaN photocathode is obtained.The maximum QE reaches 13.0% at 290 nm.According to the t-mode QE equation solved from the diffusion equation,the QE curve is fitted.From the fitting results,the electron escape probability is 0.32,the back-interface recombination velocity is 5×104 cm·s-1,and the electron diffusion length is 116 nm.Based on these parameters,the influence of GaN thickness on t-mode QE is simulated.The simulation shows that the optimal thickness of GaN is 90 nm,which is better than the 150-nm GaN.     

Clinotron的初步理论和数值模拟

在理论分析的基础上,模拟研究了微电真空太赫兹器件Clinotron。求解了色散方程,获得该器件的基本结构参数和性能参数;在考虑空间电荷场和电子回旋运动的情况下,得出能使器件内片状束稳定传输的周期永磁聚焦的磁场条件;利用3维全电磁粒子模拟程序对Clinotron进行了初步模拟以及优化。数值模拟结果表明：当输入电压为4.5 kV、发射束流大小为190 mA、输入电功率为855 W时, 运行频率为218 GHz的Clinotron的输出平均功率40 W,功率转换效率达4.68%。     

Time-dependent numerical simulation of ablation-controlled arcs

A zero-dimension (0-D) time-dependent code (ZEUS) developed to simulate ablation-controlled arc (ACA) behavior is discussed. The code includes energy transport, equation-of-state, and electrical resistivity models. Particular attention is given to the equation-of-state and the determination of the charged state of multicomponent plasma under local thermodynamic equilibrium (LTE) conditions. The 0-D model is self-consistently solved by the fourth-order Runge-Kutta method. The numerical simulation of ZEUS was compared with both experimental and other theoretical results. Comparison with experimental results demonstrates that the numerical simulation can correctly predict the behavior of ACAs     

Clinotron的初步理论和数值模拟

在理论分析的基础上,模拟研究了微电真空太赫兹器件Clinotron。求解了色散方程,获得该器件的基本结构参数和性能参数;在考虑空间电荷场和电子回旋运动的情况下,得出能使器件内片状束稳定传输的周期永磁聚焦的磁场条件;利用3维全电磁粒子模拟程序对Clinotron进行了初步模拟以及优化。数值模拟结果表明:当输入电压为4.5 kV、发射束流大小为190 mA、输入电功率为855 W时, 运行频率为218 GHz的Clinotron的输出平均功率40 W,功率转换效率达4.68%。     

PSTM成像的FDTD数值模拟

尝试用时域有限差分法(FDTD)分析采用不同探针时光子扫描隧道显微镜(PSTM)成像的分辨率和效率。对四种探针,即不镀膜,带菱形金尖,镀金膜有孔径,镀金膜无孔径的探针,用二维p极化波,满足全反射条件,并用样品台上方平行于界面的隐失波作为等效入射波源,用探针距离尖顶一定高度截面的玻印亭矢量计算散射场强。数值模拟结果表明,带纳米尺度金尖的探针具有最好成像的分辨率和效率,镀膜无孔径和镀膜孔径探针次之,不镀膜探针最差。     

Microscopic simulation of semiconductor lasers at telecommunication wavelengths

We consider two GaAs-based laser materials emitting at telecommunication wavelengths, namely the dilute nitride (GaIn)(NAs) as well as Ga(AsSb), and model their optical properties by including scattering and dephasing on a microscopic basis. The theory shows an excellent agreement with experiment without the inclusion of fit parameters such as phenomenological scattering times. By careful comparison of measurements and computations, one can extract controversial bandstructure parameters such as the band offset.