Si(111)衬底无微裂GaN的MOCVD生长

采用AlN插入层技术在Si(111)衬底上实现无微裂GaN MOCVD生长.通过对GaN外延层的a,c轴晶格常数的测量,得到了GaN所受张应力与AlN插入层厚度的变化关系.当AlN厚度在7～13nm范围内,GaN所受张应力最小,甚至变为压应力.因此,GaN微裂得以消除.同时研究了AlN插入层对GaN晶体质量的影响,结果表明,许多性能相比于没有AlN插入层的GaN样品有明显提高.     

AlGaN/GaN材料HEMT器件优化分析与I-V特性

在考虑Al Ga N / Ga N异质结中的压电极化和自发极化效应的基础上,自洽求解了垂直于沟道方向的薛定谔方程和泊松方程.通过模拟计算,研究了Al Ga N / Ga N HEMT器件掺杂层Al的组分、厚度、施主掺杂浓度以及栅偏压对二维电子气特性的影响.用准二维物理模型计算了Al Ga N/ Ga N HEMT器件的输出特性,给出了相应的饱和电压和阈值电压,并对计算结果和Al Ga N/ Ga N HEMT器件的结构优化进行了分析.     

不同AlGaN层厚度的AlGaN/GaN高电子迁移率晶体管的静态特性

利用金属有机化合物气相外延技术研究了Al Ga N/ Ga N高电子迁移率晶体管(HEMT)结构的外延生长及器件制作,重点比较了具有不同Al Ga N层厚度的HEMT器件的静态特性.实验发现具有较薄Al Ga N隔离层的结构表现出较好的器件特性.栅长为1μm的器件获得了6 5 0 m A/ m m的最大饱和电流密度和10 0 m S/ mm的最大跨导.     

调制掺杂AlxGa1-xN/GaN异质结中AlxGa1-xN势垒层表面态及其他局域态性质研究

通过测量调制掺杂Al0.22Ga0.78N/GaN异质结样品的变频电容-电压(C-V)特性,对Al0.22Ga0.78N势垒层表面态的性质进行了研究.结果发现在小偏压下,样品的电容随着测量信号频率的增加而下降,说明势垒层中存在表面态.实验数据分析表明:表面态密度约为1013cm-2量级,表面态的时间常数比势垒层中其他局域态大.随着空间隔离层厚度的增加,势垒层中其他局域态密度随之增加.在金属电极和Al0.22Ga0.78N势垒层之间加入Si3N4绝缘层可以对表面态起到显著的钝化作用,使表面态密度降为～1012cm-2量级.     

MOCVD生长的InGaN薄膜的离子束背散射沟道及其光致发光

采用 MOCVD技术以 Al2 O3为衬底在 Ga N膜上生长了 In Ga N薄膜 .以卢瑟福背散射 /沟道 (RBS/Channeling)技术和光致发光 (PL )技术对 Inx Ga1 - x N / Ga N / Al2 O3样品进行了测试 ,获得了合金层的组分、厚度、元素随深度分布、结晶品质及发光性能等信息 .研究表明生长温度和 TMIn/ TEGa比对 In Ga N薄膜的 In组分和生长速率影响很大 .在一定范围内 ,降低 TMIn/ TEGa比 ,In Ga N膜的生长速率增大 ,合金的 In组分反而提高 .降低生长温度 ,In Ga N膜的 In组分提高 ,但生长速率基本不变 . In Ga N薄膜的结晶品质随 In组分的增大而显著下降 ,In Ga N薄膜     

调制掺杂Al_xGa_(1-x)N/GaN异质结中Al_xGa_(1-x)N势垒层表面态及其他局域态性质研究

通过测量调制掺杂Al0 2 2 Ga0 78N/GaN异质结样品的变频电容电压(C V)特性,对Al0 2 2 Ga0 78N势垒层表面态的性质进行了研究.结果发现在小偏压下,样品的电容随着测量信号频率的增加而下降,说明势垒层中存在表面态.实验数据分析表明:表面态密度约为10 13 cm-2 量级,表面态的时间常数比势垒层中其他局域态大.随着空间隔离层厚度的增加,势垒层中其他局域态密度随之增加.在金属电极和Al0 2 2 Ga0 78N势垒层之间加入Si3 N4绝缘层可以对表面态起到显著的钝化作用,使表面态密度降为～10 12 cm-2 量级     

肖特基C-V法研究Al_xGa_(1-x)N/GaN异质结界面二维电子气

通过对 Pt/ Al0 .2 2 Ga0 .78N/ Ga N肖特基二极管的 C- V测量 ,研究分析了 Al0 .2 2 Ga0 .78N/ Ga N异质结界面二维电子气 (2 DEG)浓度及其空间分布 .测量结果表明 ,Al0 .2 2 Ga0 .78N/ Ga N异质结界面 2 DEG浓度峰值对应的深度在界面以下 1.3nm处 ,2 DEG分布峰的半高宽为 2 .3nm ,2 DEG面密度为 6 .5× 10 1 2 cm- 2 .与 Alx Ga1 - x As/ Ga As异质结相比 ,其 2 DEG面密度要高一个数量级 ,而空间分布则要窄一个数量级 .这主要归结于 Alx Ga1 - x N层中～ MV / cm量级的压电极化电场和自发极化电场对 Alx Ga1 - x N/ Ga N异质结能带的调制和 Alx Ga1 -     

纳米Al夹层Ga_2O_3深紫外透明导电膜的研究

用磁控溅射法在室温条件下制备了Al膜、Ga2O3膜及Ga2O3/Al/Ga2O3三层膜,对其光学和电学性能进行了表征。单层Al膜厚度大于7nm时,光学透射率在近紫外光区域大于可见光区域;Ga2O3膜在深紫外光区域(<300nm)透明,光学带隙4.96eV;Ga2O3/Al/Ga2O3三层膜透射率截止波长在245nm左右,随着顶层Ga2O3厚度增加,电导率减小,紫外光透射率峰位、吸收边、截止波长红移,透射率峰值先稍微增加,然后逐渐降低。顶层Ga2O3厚度为34nm时,Ga2O3/Al/Ga2O3三层膜在275nm处的透射率达70%,电导率为3346S.cm–1。     

Ⅲ族氮化物外延层中的缺陷

采用光荧光和阴极荧光方法 ,对 Ga N外延层中的黄色和蓝色发光进行测量分析 ;同时 ,采用原子力显微镜、扫描电镜及其能谱测量外延层中的缺陷。结果表明 ,黄色和蓝色发光与残留杂质有关。采用第一原理计算结果显示 ,残留 C、O杂质、本征缺陷等是黄色和蓝色的可能物理起源。采用原子力显微镜、扫描电镜、透射电镜及其能谱对 Ga N/Al Ga N异质结中的纳米管进行观测 ,了解了纳米管的形貌。结果表明 ,构成纳米管的小面可能是外延过程中表面吸附引起的 ;计算结果显示 ,纳米管形貌变化与 Ga N/Al Ga N界面处晶格失配应力有关。采用透射电镜观察外延层中沉积物及其周围位错的结构表明 ,沉积物附近应力的存在是位错产生的主要原因     

高Al组分N-AlxGa1-xN材料的欧姆接触

基于各层金属间在快速热退火时容易合金化及Ti,Al易被氧化的特点,在高Al组分N-AlxGa1-xN(x≥0.45)材料上溅射生长多层金属Ti/Al/Ti/Au,并且变化Ti,Al比例以及改变退火温度和时间,得到了金属与高Al组分N-AlxGa1-xN(x≥0.45)材料间的欧姆接触,由传输线模型方法测试得比接触电阻为4.9×10-2 Ω·cm2.实验中用到的样品为P(Al0.45Ga0.55N)/i(Al0.45Ga0.55N)/N-Al0.63Ga0.37N多层结构的材料.最后,利用伏安特性和俄歇电子能谱深度分布(AES)研究金属与高Al组分的材料之间形成欧姆接触的原因.     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Nanoimprint Lithography -A Next Generation High Volume Lithography Technique

IntroductionNanoimprint Lithography is a well-acknowl-edged low cost, high resolution, large area pattern-ing process. It includes the most promising methods,high-pressure hot embossing lithography (HEL) [2],UV-cured imprinting (UV-NIL) [3] and micro contactprinting (m-CP, MCP) [4]. Curing of the imprintedstructures is either done by subsequent UV-lightexposure in the case of UV-NIL or by cooling downbelow the glass transition temperature of the ther-moplastic material in case of HEL…     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.     

Influence of PVK ： NPB hole transporting layer on the characteristics of organic light-emitting devices

A doping system consisting of NPB and PVK is employed as a composite hole transporting layer （CHTL）. By adjusting the component ratio of the doping system, a series of devices with different concentration proportion of PVK ： NPB are constracted. The result shows that doping concentration of NPB enhances the competence of hole transporting ability, and modifies the recombination region of charge as well as affects the surface morphology of doped film. Optimum device with a maximum brightness of 7852 cd/m^2 and a power efficiency of 1.75 lm/W has been obtained by choosing a concentration proportion of PVK ： NPB at 1：3.     

New insert layer structure OLEDs

An insert layer structure organic electroluminescent device（OLED） based on a new luminescent material （Zn（salen）） is fabricated. The configuration of the device is ITO/CuPc/NPD/Zn（salen）/Liq/LiF/A1/CuPc/NPD/Zn（salen）/Liq/LiF/A1. Effective insert electrode layers comprising LiF（1nm）/Al（5 nm） are used as a single semitransparent mirror, and bilayer cathode LiF（1 nm）/A1（100 nm） is used as a reflecting mirror. The two mirrors form a Fabry-Perot microcavity and two emissive units. The maximum brightness and luminous efficiency reach 674 cd/m^2 and 2.652 cd/A, respectively, which are 2.1 and 3.7 times higher than the conventional device, respectively. The superior brightness and luminous efficiency over conventional single-unit devices are attributed to microcavity effect.     

Analysis of error performance on Turbo coded FDPIM

Due to variable symbol length of digital pulse interval modulation（DPIM）, it is difficult to analyze the error performances of Turbo coded DPIM. To solve this problem, a fixed-length digital pulse interval modulation（FDPIM） method is provided. The FDPIM modulation structure is introduced. The packet error rates of uncoded FDPIM are analyzed and compared with that of DPIM. Bit error rates of Turbo coded FDPIM are simulated based on three kinds of analytical models under weak turbulence channel. The results show that packet error rate of uncoded FDPIM is inferior to that of uncoded DPIM. However, FDPIM is easy to be implemented and easy to be combined, with Turbo code for soft-decision because of its fixed length. Besides, the introduction of Turbo code in this modulation can decrease the average power about 10 dBm, which means that it can improve the error performance of the system effectively.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.