质量分离低能离子束外延超薄硅单晶的初步研究

于2010-11-23批量导入

一种新的非均匀减薄法-选择阳极氧化法

于2010-11-23批量导入

A novel high sensitivity CE-PTHPT for optical fiber communication

Planar punch through heterojunction phototransistors with a novel emitter control electrode and ion- implanted isolation (CE-PTHPT) are investigated. The phototransistors have a working voltage of 3-10V and high sensitivity at low input power. The base of the transistor is completely depleted under operating condition. Base current is zero. The CE-PTHPT has an increased speed and a decreased noise. The novel CE-PTHPT has been fabricated in this paper. The optical gain of GaAlAs/GaAs CE-PTHPT for the incident light power 1.3 and 43nw with the wavelength of 0.8 mu m reached 1260 and 8108. The input noise current calculated is 5.46 x 10(-16) A/H-z(1/2). For polysilicon emitter CE-PTHPT, the optical gain is 3083 at the input power of 0.174 mu w. The optical gain of InGaAs/InP CE-PTHPT reaches 350 for an incident power of 0.3 mu w at the wavelength of 1.55 mu m. The CE-PTHPT detectors is promising as photo detectors for optical fiber communication system.

Effects and numerical analysis of argon gas flow on the oxygen concentration in Czochralski silicon single crystal growth

Argon gas, as a protective environment and carrier of latent heat, has an important effect on the temperature distribution in crystals and melts. Numeric simulation is a potent tool for solving engineering problems. In this paper, the relationship between argon gas flow and oxygen concentration in silicon crystals was studied systematically. A flowing stream of argon gas is described by numeric simulation for the first time. Therefore, the results of experiments can be explained, and the optimum argon flow with the lowest oxygen concentration can be achieved. (C) 2002 Elsevier Science B.V. All rights reserved.

In situ annealing treatment and In-doping of GaN epilayers grown by MOVPE

The effects of in situ annealing treatment in the initial growth stage and In-doping during growth of the GaN on the material properties were investigated. GaN was grown by LP-MOVPE. In situ annealing reduced the full-width at half-maximum (FWHM) of X-ray rocking curves and reduced etch pit density of GaN films. It improved the optical properties of the epilayer. Undoped and In-doped GaN films of initial growth stage were investigated. It was found that morphology and optical properties were improved in In-doped samples. (C) 2000 Elsevier Science B.V. All rights reserved.

Fe-57 Mossbauer spectroscopic and magnetic studies of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

Mossbauer spectra for Fe atoms in the series of R3Fe29-xVx (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) compounds were collected at 4.2 K. The ratio of 14.5 T/mu(B) between the average hyperfine field B-hf and the average Fe magnetic moment mu(Fe)(MS), obtained from our data, in Y3Fe29-xVx is in agreement with that deduced from the RxTy alloys by Gubbens et al. The average Fe magnetic moments mu(Fe)(MS) in these compounds at 4.2 K, deduced from our Mossbauer spectroscopic studies, are in accord with the results of magnetization measurement. The average hyperfine field of the Fe sites for R3Fe29-xVx at 4.2 K increases with increasing values of the rare earth effective spin (g(J) - 1) J, which indicates that there exists a transferred spin polarization induced by the neighboring rare earth atom.

Improved neutron radiation hardness for Si detectors: Application of low resistivity starting material and or manipulation of N-eff by selective filling of radiation-induced traps at low temperatures

Radiation-induced electrical changes in both space charge region (SCR) of Si detectors and bulk material (BM) have been studied for samples of diodes and resistors made on Si materials with different initial resistivities. The space charge sign inversion fluence (Phi(inv)) has been found to increase linearly with the initial doping concentration (the reciprocal of the resistivity), which gives improved radiation hardness to Si detectors fabricated from low resistivity material. The resistivity of the BM, on the other hand, has been observed to increase with the neutron fluence and approach a saturation value in the order of hundreds k Omega cm at high fluences, independent of the initial resistivity and material type. However, the fluence (Phi(s)), at which the resistivity saturation starts, increases with the initial doping concentrations and the value of Phi(s) is in the same order of that of Phi(inv) for all resistivity samples. Improved radiation hardness can also be achieved by the manipulation of the space charge concentration (N-eff) in SCR, by selective filling and/or freezing at cryogenic temperatures the charge state of radiation-induced traps, to values that will give a much smaller full depletion voltage. Models have been proposed to explain the experimental data.

基于物理的植物叶子形态变化过程仿真造型

文中提供了一种对植物叶子造型的新方法,可以非常真实地展现叶子在干枯、老化过程中几何形态的变化.基于植物学和物理原理,文中引入了双层结构模型表达叶子的力学结构,很好地模拟了不同种类植物叶子形状的多样性.文中首先分析了叶子形状变化的原因,即在叶子枯萎过程中,叶肉和叶脉由于各自不同的组织结构,导致了收缩比例不同,从而在物理模拟中,通过建立关于叶子基本结构的双层质点-弹簧模型,并对上下两层的不同参数的合理设置,很好地表现了叶肉和叶脉的不同力学特性.双层模型的相互作用,决定了叶子最终变形的方式和效果,由此可以得到非常接近真实树叶的各种叶子形态.

基于注释改进动态需求跟踪的方法

需求跟踪为软件工程提供有力的支持,然而人工建立需求跟踪关系费时费力,存在着成本过高,难以维护等问题.动态需求跟踪运用信息检索等技术,自动化建立需求文档和工作产品的跟踪关系,但在跟踪精度等方面仍然存在问题.在现有的动态需求跟踪方法基础之上,分析了需求动态跟踪精度问题产生的原因,提出了使用代码注释辅助动态需求跟踪的方法,改进了需求动态跟踪工具,并通过实验验证了方法对于动态需求跟踪效果的改进.

长白山北坡岳桦云冷杉林中倒木在森林天然更新中的作用

长白山岳桦云冷杉林是我国北部亚高山地段罕见的森林植被之一。林下有大量的倒木。倒木株数和生物量分别为509株/ha和33.82吨/ha，主要以鱼鳞云杉为主，多数处于中度腐烂时期。在这种森林中，由于林地苔藓，草本植物对幼苗的竞争以及雨季水湿对种子，苗木的胁迫，所以倒木是该森林的主要苗床。虽倒木的覆盖面积只占林地面积的7.21%，但其上所着生的幼苗株数却占林内幼苗总数的82.45%。倒木只有腐烂至一定程度，而表层的苔藓又不至于达到对幼苗造成胁迫时，才是好的苗床。一般地倒木表层腐殖质的厚度是和倒木的腐烂程度一致的。只有表面腐殖质较厚的大直径腐朽木适合于种子发芽和幼苗生长，所以这里将腐烂倒木的覆盖面积定义为“倒木对更新的有效面积”，它和“倒木分布均匀度”共同影响森林的天然更新。除倒木外、根桩、腐烂根盘堆、林地等也是林下幼苗的更新基质。随着幼苗的生长，自然稀疏开始。在从幼苗到幼树及成树的发展过程中，各树种在不同基质上的株数以不同的指数模式减少。尽管生长于倒木上的植株，在苗期有相对较高的死亡率，但和生长于其它基质上的植株数相比，倒木上着生的树木始终占大多数。倒木上的植株不仅苗期数量大，而且成林率高。