INVESTIGATION OF C-60 SINGLE-CRYSTAL BY X-RAY-METHODS

C-60 Single crystals grown by a single-temperature-gradient technique were characterized by synchrotron radiation white beam x-ray topography and x-ray double crystal diffraction with Cu K-alpha 1 radiation on conventional x-ray source. The results show that the crystal is rather well crystallized, The x-ray topographies give an evidence of dendritic growth mechanism of C-60 Single crystal, and x-ray double crystal diffraction rocking curve shows that there are mosaic structural defects in the sample. A phase transition st 249+/-1.5% K from a simple cubic to a face centered cubic structure is confirmed by in situ observation of synchrotron radiation white beam x-ray topography with the temperature varing from 230 to 295 K.

Zn-doped InGaAs Base Heterojunction Bipolar Transistors Grown by Low Pressure Metal Organic Chemical Vapor Deposition

High performance InP/InGaAs heterojunction bipolar transistors(HBTs) have been widely used in high-speed electronic devices and optoelectronic integrated circuits. InP-based HBTs were fabricated by low pressure metal organic chemical vapor deposition(MOCVD) and wet chemical etching. The sub-collector and collector were grown at 655 ℃ and other layers at 550 ℃. To suppress the Zn out-diffusion in HBT, base layer was grown with a 16-minute growth interruption. Fabricated HBTs with emitter size of 2.5×20 μm~2 showed current gain of 70~90, breakdown voltage(BV_(CE0))>2 V, cut-off frequency(f_T) of 60 GHz and the maximum relaxation frequency(f_(MAX)) of 70 GHz.

High-speed electrooptical VOA integrated in silicon-on-insulator

In this paper, we present simulation results of an electrooptical variable optical attenuator (VOA) inte-grated in silicon-on-insulator waveguide. The device is functionally based on free carriers absorption toachieve attenuation. Beam propagation method (BPM) and two-dimensional semiconductor device simu-lation tool PISCES-Ⅱ were used to analyze the dc and transient characteristics of the device. The devicehas a response time (including rise time and fall time) less than 200 ns, much faster than the thermoopticand micro-electromechanical systems (MEMSs) based VOAs.

纳米硅(nc-Si:H )/晶体硅(c-Si)异质结太阳电池的数值模拟分析

运用美国宾州大学发展的AMPS程序模拟分析了n-型纳米硅(n+-nc-Si:H)/p-型晶体硅(p-c-Si)异质结太阳电池的光伏特性.分析表明,界面缺陷态是决定电池性能的关键因素,显著影响电池的开路电压(VOC)和填充因子(FF),而电池的光谱响应或短路电流密度(JSC)对缓冲层的厚度较为敏感.对不同能带补偿(bandgap offset)的情况所进行的模拟分析表明,随着ΔEc的增大,由于界面态所带来的开路电压和填充因子的减小逐渐被消除,当ΔEc达到0.5eV左右时界面态的影响几乎完全被掩盖.界面层的其他能带结构特征对器件性能的影响还有待进一步研究.最后计算得到了这种电池理想情况下(无界面态、有背面场、正背面反射率分别为0和1)的理论极限效率ηmax=31.17% (AM1.5,100mW/cm2,0.40-1.10μm波段).

快速热退火和氢等离子体处理对富硅氧化硅薄膜微结构与发光的影响

采用micro-Raman散射、傅里叶变换红外吸收谱和光致发光谱研究了快速热退火及氢等离子体处理对等离子体增强化学气相沉积法200 ℃衬底温度下生长的富硅氧化硅（SRSO）薄膜微结构和发光的影响。研究发现在300-600 ℃范围内退火，SRSO薄膜中非晶硅和SiO_x:H两相之间的相分离程度随退火温度升高趋于减小；而在600-900 ℃范围内退火，其相分离程度退火温度升高又趋于增大；同时发现SRSO薄膜发光先是随退火温度的升高显著加强，然后在退火温度达到和超过600 ℃后迅速减弱；发光峰位在300 ℃退火后蓝移，此后随退火温度升高逐渐红移。对不同温度退火后的薄膜进行氢等离子体处理，发光强度不同程度有所增强，发光峰位有所移动，但不同温度退火样品发光增强的幅度和峰位移动的趋势不同。分析认为退火能够引起薄膜中非晶硅颗粒尺度、颗粒表面结构状态以及氢的存在和分布等方面的变化。结果表明不仅颗粒的尺度大小，而且颗粒表面的结构状态都对非晶硅颗粒能带结构和光生载流子复合机理发挥重要影响。

氢化非晶硅氧薄膜微结构

以Raman散射、X射线电子能谱和红外吸了光谱细致研究了PECVD法250℃衬底温度下制备的氢化非晶硅氧（a-SiOx:H)薄膜的微结构及键构型。研究表明，在0．52≤x≤1.58的氧含量范围内，a-SiOx:H薄膜成分和结构不是均一的，依赖于局域键构型氧化程度的不同，大致存在着5种在一定程度上相互分离的结构组分，即Si,Si2O(:H),SiO(:H),Si2O3(:H)和SiO2。其中的Si相以非氢化的非晶硅（a-Si)颗粒形式存在，随氧含量x的增加其尺度持续减小但始终存在。提出一种多壳层模型来描述a-SiOx:H薄膜的结构，认为a-SiOx:H薄膜中a-Si颗粒依次为Si2O(:H),SiO(:H),Si2O3(:H)和SiO2壳层所包围。随薄膜氧含量x的增加，各壳层厚度相应变化但各自的化学构成基本保持不变。

半导体纳米结构的可控生长

应用MBE技术和SK生长模式，通过对研究材料体系的应力分布设计，生长动力学研究和生长工艺优化，实现了In(Ga)As/GaAs,InAlAs/AlGaAs/GaAs和InAs/InAl(Ga)As/InP无缺陷量子点（线）的尺寸、形状、密度和分布有序性的可控生长，这对进一步的器件应用特别重要。讨论了半导体纳米结构的空间有序性分布物理起因和退火的机制。

GaInNAs/GaAs量子阱的光致发光谱和光调制反射谱

研究了GaInNAs/GaAs多量子阱在不同温度和激发功率下的光致发光（PL）谱以及光调制反射（PR）谱。发现PL谱主发光峰的能量位置随温度的变化不满足Varshni关系，而是呈现出反常的S型温度依赖关系。进一步测量，特别是在较低的激发光功率密度下，发现有两个不同来源的发光峰，它们分别对应于氮引起的杂质束缚态和带间的激子复合发光。随温度变化，这两个发光峰相对强度发生变化，造成主峰（最强的峰）的位置发生切换，从而导致表观上的S型温度依赖关系。采用一个基于载流子热激发和出空过程的模型来解释氮杂质团簇引起的束缚态发光峰的温度依赖关系。

立方相GaN/GaAs（001）外延层中六角相的分布特征

于2010-11-23批量导入

Determination of interstitial oxygen concentration in heavily doped silicon by combination of neutron irradiation and FTIR

于2010-11-23批量导入

Influence of precipitates on GaN epilayer quality

GaN epilayers grown on pre-nitridated (0001) sapphire substrates by metallorganic vapor phase epitaxy were investigated by wavelength dispersive X-ray spectroscopy and energy dispersive S-ray spectroscopy. Precipitates were observed to mainly consist of O impurity whose strengths were weaker than surrounding matrix. The precipitates were larger in size and distributed more sparsely and inhomogeneously in < 11-20 > directions of the epilayers grown on substrates pre-nitridated for longer periods. The larger precipitates often joined to cracks in the TEM specimens. The crack formation seems to be attributed to the compressive stress concentration at edge angles of the larger precipitates. Yellow luminescence of the epilayers was imaged by cathodoluminescence. The distribution similarity between the cathodoluminescence and the precipitates suggested that the precipitates were responsible for the yellow luminescence band. (C) 2000 Elsevier Science S.A, All rights reserved.

Methods to tune the electronic states of self-organized InAs/GaAs quantum dots

After capping InAs islands with a thin enough GaAs layer, growth interruption has been introduced. Ejected energy of self-organized InAs/GaAs quantum dots has been successfully tuned in a controlled manner by changing the thickness of GaAs capping layer and the time of growth interruption and InAs layer thickness. The photoluminescence (PL) spectra showing the shift of the peak position reveals the tuning of the electronic states of the QD system. Enhanced uniformity of Quantum dots is observed judging from the decrease of full width at half maximum of FL. Injection InAs/GaAs quantum dot lasers have been fabricated and performed on various frequencies. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

杂谷脑流域景观格局优化配置研究

景观格局优化理论、方法和技术的研究是景观生态学的一个热点问题，同时也是一个难点。本文以眠江上游典型研究区-杂谷脑流域为研究对象，利用遥感和GIS技术分析该流域从1974年到2000年景观格局的时空变化，并分析了对该流域生态安全存在威胁的主要因素；以空间模拟技术和线性规划为基础建模，从理论和方法上探讨景观格局优化配置问题，以期为该区域的农林复合景观系统的生态安全和可持续发展找出切实可行的格局优化模式；并提出生态敏感度概念，为景观管理优先级提供依据。本文的主要结论如下：（l）杂谷脑流域作为长江上游重要的森林资源输出地，从1974年到2000年景观变化得出，有林地面积减少13％；灌木林地面积增加37％；相应的水源涵养能力下降，土壤侵蚀量增加7.8％；（2）杂谷脑流域陡坡耕作严重，分布在20°-45°坡度上的耕地占耕地总面积的78．2％；干旱河谷分布范围扩大，面积从1974年的217.99km2增加到2000年的237．38kmZ对生态安全造成威胁；（3）产业结构以资源密集型产业和重污染工业为主，结构不合理，第一产业比例大，农民人均纯收入远低于同期全国平均水平，教育水平比较低，这些问题会对杂谷脑流域生态安全产生负向影响；（4）以减少土壤侵蚀为依据，通过空间建模和线性规划方法优化设计杂谷脑流域景观格局，优化结果显示土壤侵蚀量比2000年减少2.35*106吨／年，土壤保持能力与1974年相近，水源涵养能力增强；（5）景观管理对于区域安全必不可少，针对该流域现存问题，建议以提高科学技术水平，调整产业结构和资源利用方式，提高教育水平为突破口。

黑土中铜的环境容量

本文以土壤一植物系统为中心，通过铜在三个类型区黑土中的作物效应，作物残毒，环境效应，封对铜的自净能力，综合确定了黑土中铜的临界含量，根据野外调查和室内模拟的各项物质平衡参数，代入数学模型，计算出不同年限黑土中铜的环境容量。作物盆栽（春小麦、大豆）试验表明，作物受铜害的起始浓度在200-400ppm以上。以作物减产10%为依据，经相关方程计算，黑土中铜作物效应的临界值为348.46ppm（全铜），和217.93ppm（有效铜，0.1N Hcl）。在本实验土壤铜浓度范围内（0-1000ppm），作物籽实，茎（叶、荚）中铜含量很少超过20ug/g毒性标准。土壤对铜的吸附一解吸试验表明，代表土壤对铜自净能力的指标一固态吸附量在本实验条件下为806.77-1456.16ug/g土。铜对环境影响试验表明，土壤投加铜1204.09ppm和土壤投加铜200ppm不导致地下水和地表水超标。综合以上各个单一体系的临界指标，选择限制性因子，确定黑土中铜的临界值为348.46ppm（全铜）。根据野外调查和模拟的各项物质平衡参数，经数学模型计算出了黑土中不同年限的变动容量（Q）和总容量（Q总）。如，t = 50年，Q = 1700.58g/亩·年，Q总 = 85029 g/亩。