MBE InAs quantum dots grown on metamorphic InGaAs for long wavelength emitting

GaAs-based InAs quantum dots using InGaAs composition-graded metamorphic layers have been investigated by molecular beam epitaxy. Emission with the wavelength similar to 1.5 mu m from the dots was obtained at room temperature with the relatively large full width at half maximum. The emission wavelength is relatively stable when subjected to fast annealing. The number density of dots reached similar to 6 x 10(10) cm(-2). Undulated morphology was observed on the surface of the sample, which has some influence on the dot size and distribution. In epilayers, misfit dislocations were confined within the step-graded InGaAs metamorphic buffer layer. (c) 2006 Elsevier B.V. All rights reserved.

Correlation of structural and optical investigation of InGaAs/InAlAs quantum cascade laser

Double X-ray diffraction has been used to investigate InGaAs/InAlAs quantum cascade (QC) laser grown on InP substrate by molecule beam epitaxy, by means of which, excellent lattice matching, the interface smoothness, the uniformity of the thickness and the composition of the epilayer are disclosed. What is more, these results are in good agreement with designed value. The largest lattice mismatch is within 0.18% and the intersubband absorption wavelength between two quantized energy levels is achieved at about lambda = 5.1 mum at room temperature. At 77 K, the threshold density of the QC laser is less than 2.6 kA/cm(2) when the repetition rate is 5 kHz and the duty cycle is 1%. (C) 2003 Elsevier Science B.V. All rights reserved.

The plasmon resonance absorption of Ag/SiO2 nanocomposite films

The plasmon resonance absorption of the Ag/SiO2 nanocomposite film is investigated. The measured absorption spectra are compared with those calculated by the Mie theory. The results indicate that the Mie theory on the basis of classical electrodynamics can only partially explain the optical absorption spectra of the Ag/SiO2 nanocomposite film. We believe that the plasmon resonance absorption is mainly an intrinsic quality of the metal particle, and can be explained only with the electronic structure of the metal particle. In the latter, surface resonance state is introduced to systematically discuss the optical absorption spectra of the Ag/SiO2 nanocomposite film. (C) 2003 Elsevier Science B.V. All rights reserved.

Metal-semiconductor-metal ultraviolet photodetector based on GaN

A metal-semiconductor-metal (MSM) ultraviolet photodetector has been fabricated using unintentionally doped n-GaN films grown on sapphire substrates. Its dark current, photocurrent under the illumination with lambda = 360 nm light, responsivity, and the dependence of responsivity on bias voltage were measured at room temperature. The dark current of the photodetector is 1.03 nA under 5 V bias, and is 15.3 nA under 10 V bias. A maximum responsivity of 0.166 A/W has been achieved under the illumination with lambda = 366 nm light and 15 V bias. It exhibits a typical sharp band-edge cutoff at the wavelength of 366 nm, and a high responsivity at the wavelength from 320 nm to 366 nm. Its responsivity under the illumination with lambda = 360 nm light increases when the bias voltage increases.

A 1Gb/s silicon photo-receiver in standard CMOS for 850-nm optical communication

A monolithic silicon CMOS optoelectronic integrated circuit (OEIC) was designed and fabricated with standard 0.6 mu m CMOS technology. This OEIC circuit consisted of an integrated double photodiode detector (DPD) and a preamplifier. The DPD detector exhibited high bandwidth by screening the bulk-generated diffusion carriers and suppressing the slow diffusion tail effect. The preamplifier exploited the regulated cascode (RGC) configuration as the input stage of receiver, thus isolating the influence of photodiode capacitance and input parasitic capacitance on bandwidth. Testing results showed that the bandwidth of OEIC was 700MHz, indicating the bit rate of 1Gb/s was achieved.

Modelica建模软件形成的高指标微分代数方程系统指标约简算法研究

随着产品设计的复杂化，应用领域中的数学建模和仿真越来越重要，传统建模方法基于赋值语句，主要考虑单一系统，工程人员需要对程序设计语言和算法求解有相当程度的熟悉，这导致了传统建模方法很难满足复杂产品设计的需要。欧洲仿真界的学者在总结现有建模方法的基础上于1997年推出了一种面向对象的、陈述式的基于方程的语言——Modelica，Modelica语言支持多领域建模，Modelica语言得到了仿真领域众多厂商的支持，成为统一建模领域的事实标准，实现Modelica仿真环境具有重大意义。 编译器是Modelica仿真环境中的核心组件，Modelica编译器会产生高指标DAE系统，除了部分特殊结构的高指标DAE，现有求解器一般不能对通用高指标DAE直接求解，现在一般做法是先对高指标DAE进行指标约简，将其转换成等价的低指标DAE，然后进行求解。这就要求Modelica编译器具有指标约简的功能，以便利用现有求解器进行求解。 本文介绍了几种现有的指标约简算法，给出了各个算法指标约简原理和约简步骤，并对这些算法进行了分析和比较，得出各自的优缺点。最后，本文设计并实现了一个指标约简系统，采用三个Modelica模型产生的方程对系统进行了测试，并验证了实验结果的正确性。

基于贝叶斯网络近似推理的网络脆弱性评估方法

针对大规模计算机网络的脆弱性评估,提出了一种基于贝叶斯网络近似推理的评估方法,对网络各组件和影响网络安全的因素进行建模,采用模型检测工具生成攻击状态转移图,描述网络脆弱性的利用过程,通过采用随机采样的方法对网络的攻击状态转移图进行近似推理,经过对采样样本的统计分析得到网络脆弱性评估的量化结果,为提升网络的安全性能提供理论依据。

基于工作流的网上协同办公系统的设计与实现

在简单介绍工作流管理系统一般概念的基础上,重点介绍了基于工作流技术实现的网上协同办公系统的体系结构、系统主要组成部分、各部门的实现方法以及需要注意的事项。

同步数据流模型调度序列的空间优化

提出了一种嵌入式DSP系统的存储优化方法。该方法基于同步数据流模型SDF(Synchronous Data Flow)。针对其他优化算法不适用于存在反馈环的同步数据流模型的问题,该方法为反馈环的空间优化设计实现了启发式的调度算法,并提出了将SAS(Single Appearance Schedules)和Non-SAS类型调度序列相结合的层次化的空间优化方案,为同步数据流模型调度序列的空间优化提供一个通用的解决方案。实验结果证实了该方案的有效性。

面向虚拟装配的三维交互平台

针对当前装配领域的特点 ,提出一个面向虚拟装配的三维交互平台 (Virtual Assem bly Toolkit,VAT) .VAT中包含了新的三维交互思想 ,定义了装配领域中常用的三维交互原语 ,设计和实现了交互原语的捕获、解释和处理框架 .同时 ,VAT封装了三维图形构造、零件间的约束和碰撞检测等功能 .VAT可以大大简化虚拟装配应用的构造 ,便于应用的快速生成