自组装法制备新型液晶垂直取向膜

用硅烷偶联剂3-氨丙基-三乙氧基硅烷,通过自组装反应在石英基板表面制备了含有二苯乙炔基的自组装单层膜。用该自组装膜作为向列相液晶的取向层制成液晶器件,在偏光显微镜下观察,发现向列相液晶获得了均匀、稳定的垂直取向效果。热稳定性试验表明,用自组装方法制备的液晶垂直取向膜有良好的热稳定性,在250℃条件下取向仍可保持。     

含炔键大双折射液晶的研究进展

阐述了形成大双折射液晶化合物的结构因素和含炔键大双折射液晶化合物的主要研究成果。迄今研究发现:二芳基取代的乙炔类(PTP)液晶双折射范围在0.25~0.49;双烷基联苯炔(PPTP)类液晶双折射范围在0.32~0.5;双苯二乙炔类(PTTP、PTDTP、PTPTP)液晶双折射范围在0.35~0.67;三联苯乙炔苯类液晶化合物双折射值约为0.54;含氰基或异硫氰基的苯炔类液晶双折射范围在0.25~0.79;稠环基苯乙炔类液晶双折射在0.36~0.79。含炔键苯类液晶材料具有较大的双折射值和实用价值。     

二苯乙炔基异硫氰酸酯的合成与液晶性质研究

通过先偶联后还原的方法合成了3种具有氟取代的二苯乙炔基异硫氰酸酯化合物。液晶性质测试表明,这些材料均具有较高的Δn值,且随着分子中π电子共轭长度增加而变大,最大可达0.576。将这些高Δn液晶化合物溶于商品炔类液晶材料,可提高其响应速度;其中苯基二苯乙炔基异硫氰酸酯对器件响应性能的提升幅度最大。实验结果表明,二苯乙炔基异硫氰酸酯是一种具有高Δn、低旋转黏度的快速液晶材料,在液晶空间光调制器件中具有一定的应用价值。     

多氟二苯乙炔类负性液晶化合物的合成

以烷基环己基酮、1,2-二氟苯为起始原料(或以2,3-二氟烷基苯为起始原料),采用正丁基锂低温下制得金属锂化试剂,再经过系列反应制得4-烷基环己基-2,3-二氟碘苯(或4-烷基-2,3-二氟碘苯),其与4-乙氧基-2,3-二氟苯乙炔发生Sonogashira偶联反应,合成出了3种2,3,2′,3′-四氟二苯乙炔类液晶化合物.进行了产品的结构标定以及参数测定,确定该类化合物有较大的光学各向异性(Δn)和负值较大的介电各向异性(Δε),并且具有较宽的相变温度范围,可以用于改善液晶材料的响应速度和驱动电压.     

2,3,4-三氟苯乙炔类液晶的合成

以2,3,4-三氟苯胺为原料,经桑德迈尔反应合成出2,3,4-三氟碘苯,2,3,4-三氟碘苯和2-甲基-3-丁炔-2-醇在四(三苯基膦)钯催化下合成4-(2,3,4-三氟苯)-2-甲基-3-丁炔-2-醇。4-(2,3,4-三氟苯)-2-甲基-3-丁炔-2-醇在氢氧化钾作用下生成2,3,4-三氟苯乙炔。2,3,4-三氟苯乙炔与6种碘代苯发生Sonogashira反应,合成出6种2,3,4-三氟二苯乙炔类液晶化合物。进行了产品结构标定以及参数的测定,确定了化合物具有较大的光学各向异性(Δn),较宽的相变温度范围。     

聚酰亚胺的侧链结构对液晶取向性能的影响

聚酰亚胺取向膜是液晶显示器的重要组成部分,对显示器件性能具有重要影响。通过实验室自行合成的两种不同侧链的二胺单体,与4,4'-二胺基二苯甲烷和均苯四羧酸二酐聚合得到含有酯键型侧链和含有醚键型侧链结构的两种聚酰亚胺。通过偏光显微镜观察,液晶分子在两种聚酰亚胺取向膜上都获得了均匀取向。测试了不同侧链结构的聚酰亚胺取向膜产生的预倾角,发现含有酯键型侧链结构的聚酰亚胺比含有醚键型侧链结构的聚酰亚胺产生的预倾角略大,且取向稳定性更好。     

彩色顺序制液晶显示器的快速液晶开关

本文中,研究制成了含有液晶材料异硫氰酸根二苯乙炔和异硫氰酸根三联苯的较高双折射(0.3<△n<0.4)和相对低粘性的液晶混合物。制作了用于顺序制彩色液晶显示器的扭曲相列式液晶薄盒(TN),盒厚为1.6μm,研究证明了其响应时间为1ms。     

未端氰基取代含氟二苯乙炔类液晶的合成与相变研究

设计并合成了一类新型末端氰基取代含氟二苯乙炔类液晶。通过偏光显微镜和DSC对其相仿进行了研究。此类化合物仅呈现一个向列相。讨论了积极效应和极性因素对液晶稳定性及相奕温度范围的影响。     

STN—LCD的新进展

STN-LCD采用新的取向层,消除了残象;采用新的驱动波形,消除了串扰;采用二(口恶)烷、卤化物、链烯基、醚和二苯乙炔,改进了液晶料材的性能,使STN-LCD获得高的对比度、快的响应速度、低的驱动电压;采用有源矩阵驱动方法,消除了帧响应,使STN-LCD获得高的对比度、高的亮度及视频响应速度;使用温度跟踪电路,自动跟踪STN-LCD的阀值电压,使STN-LCD获得宽的工作温度。     

含氟二苯乙炔类液晶材料的合成和性质研究

从烷基苄氯和对氟苯甲醛开始,用Ｗｉｔｉｎｇ－Ｈｏｒｎｅｒ反应合成了１,２－二苯乙烯,再加成一分子溴,然后脱去两分子溴化氢,将双键转变成三键,合成了末端为单氟和碳原子数分别为３,４,５,６正构烷基链的４种三环二苯乙炔类化合物。４种化合物分别具有从８５～１０１℃宽的向列相温度范围。     

Characteristics of Green Light-Emitting Diodes Using an InGaN:Mg/GaN:Mg Superlattice as p-Type Hole Injection and Contact Layers

Mg-doped InGaN/GaN p-type short-period superlattices (SPSLs) are developed for hole injection and contact layers of green light-emitting diodes (LEDs). V-defect-related pits, which are commonly found in an InGaN bulk layer, can be eliminated in an InGaN/GaN superlattice with thickness and average composition comparable to those of the bulk InGaN layer. Mg-doped InGaN/GaN SPSLs show significantly improved electrical properties with resistivity as low as ∼0.35 ohm-cm, which is lower than that of GaN:Mg and InGaN:Mg bulk layers grown under optimized growth conditions. Green LEDs employing Mg-doped InGaN/GaN SPSLs for hole injection and contact layers have significantly lower reverse leakage current, which is considered to be attributed to improved surface morphology. The peak electroluminescence intensity of LEDs with a SPSL is compared to that with InGaN:Mg bulk hole injection and contact layers.     

使用溅射AlN成核层实现大规模生产深紫外LED

高质量AlN薄膜对制造高性能深紫外器件非常重要,但是目前还很难使用大型工业MOCVD生长出高质量的AlN薄膜.采用磁控溅射制备了不同厚度的用作成核层的AlN薄膜,使用大型工业MOCVD直接在成核层上高温生长AlN外延层,研究了不同成核层对AlN外延层质量的影响.通过扫描电子显微镜和原子力显微镜对成核层AlN薄膜的表面形貌进行表征;使用高分辨X射线衍射仪对AlN外延层晶体质量进行表征,结果表明:在溅射成核层上生长的AlN外延层的晶体质量有显著提高.使用大型工业MOCVD在蓝宝石衬底上成功制备出中心波长为282 nm的可商用深紫外LED,在注入电流为20 mA时,单颗深紫外LED芯片的光输出功率达到了1.65 mW,对应的外量子效率为1.87%,饱和光输出功率达到4.31 mW.     

理想匹配层的综合优化

本文讨论了理想匹配层的吸收性能 ,给出了一种有效截断理想匹配层的边界条件 ,分析了不同导率剖面和边界条件对理想匹配层吸收性能的影响 ,给出了最小反射意义下的优化理想匹配层。     

Structural defects in Si-doped III–V nitrides

Transmission electron microscopy has been used to study undoped and Si-doped InGaN/GaN layers. The doped layers show formation of extrinsic dislocation loops. These defects are not formed in the undoped samples. The highly Si-doped layers show failure of selective photoelectrochemical wet-etching used for device fabrication. This loss of etching selectivity is attributed to Si-induced defects evenly distributed in the InGaN layers and their vicinities.     

Comparison of GaN and In<Subscript>0.04</Subscript>Ga<Subscript>0.96</Subscript>N <Emphasis Type="Italic">p</Emphasis>-Layers on the Electrical and Electroluminescence Properties of Green Light Emitting Diodes

We have compared the effects of Mg-doped GaN and In_0.04Ga_0.96N layers on the electrical and electroluminescence (EL) properties of the green light emitting diodes (LEDs). To investigate the effects of different p-layers on the LED performance, the diode active region structures were kept identical. For LEDs with p-InGaN layers, the p-In_0.04Ga_0.96N/GaN polarization-related EL peak was dominant at low current levels, while the multiple-quantum-well (MQW) peak became dominant at higher current levels, different from LEDs with p-GaN layers. Also, LEDs with p-InGaN exhibited slightly higher turn on voltages (V _on ) and forward voltages (V _f ) compared to LEDs with p-GaN layers. However, the MQW related EL intensity was much higher and diode series resistance lower for LEDs with p-InGaN layers compared with LEDs with p-GaN, showing possible improvements in output power for LEDs with p-InGaN layers. The diodes with p-GaN layers typically showed V _f of ∼3.1 V at a drive current of 20 mA, with a series resistance of ∼24.7 Ω, while diodes with p-InGaN showed V _f of ∼3.2 V, with a series resistance of ∼18.5 Ω, for device dimensions of 230 μm by 230 μm.     

Influence of growth temperature and growth rate of p-GaN layers on the characteristics of green light emitting diodes

We investigated the electrical and structural qualities of Mg-doped p-type GaN layers grown under different growth conditions by metalorganic chemical vapor deposition (MOCVD). Lower 300 K free-hole concentrations and rough surfaces were observed by reducing the growth temperature from 1,040°C to 930°C. The hole concentration, mobility, and electrical resistivity were improved slightly for Mg-doped GaN layers grown at 930°C with a lower growth rate, and also an improved surface morphology was observed. In_0.25Ga_0.75N/GaN multiple-quantum-well light emitting diodes (LEDs) with p-GaN layers grown under different conditions were also studied. It was found from photoluminescence studies that the optical and structural properties of the multiple quantum wells in the LED structure were improved by reducing the growth temperature of the p-layer due to a reduced detrimental thermal annealing effect of the active region during the GaN:Mg p-layer growth. No significant difference in the photoluminescence intensity depending on the growth time of the p-GaN layer was observed. However, it was also found that the electroluminescence (EL) intensity was higher for LEDs having p-GaN layers with a lower growth rate. Further improvement of the p-GaN layer crystalline and structural quality may be required for the optimization of the EL properties of long-wavelength (∼540 nm) green LEDs.     

基于全卷积神经网络的SAR图像目标分类

近年来,卷积神经网络(Convolutional Neural Network,CNN)在合成孔径雷达(Synthetic Aperture Radar,SAR)图像目标分类中取得了较好的分类结果。CNN结构中,前面若干层由交替的卷积层、池化层堆叠而成,后面若干层为全连接层。全卷积神经网络（All Convolutional Neural Network, A-CNN）是对CNN结构的一种改进,其中池化层和全连接层都用卷积层代替,该结构已在计算机视觉领域被应用。针对公布的MSTAR数据集,提出了基于A-CNN的SAR图像目标分类方法,并与基于CNN的SAR图像分类方法进行对比。实验结果表明,基于A-CNN的SAR图像目标分类正确率要高于基于CNN的分类正确率。     

Effect of thin strain-compensated Al0.6Ga0.4P layers on the growth of multiple-stacked InP/In0.5Al0.3Ga0.2P quantum dots

Multiple-stacked InP self-assembled quantum dots (SAQD or QD) were grown on an In_0.5Al_0.3Ga_0.2P matrix lattice-matched on a GaAs (001) substrate using metalorganic chemical vapor deposition. Cathodoluminescence (CL) scanning electron microscopy, and transmission electron microscopy were employed to characterize the optical, morphological, and structural properties of the grown QDs. We found that the CL line width broadens and the surface becomes rough with an increase in the number of stacked QD layers in the structure. However, by introducing thin tensile-strained Al_0.6Ga_0.4P layers in the middle of In_0.5Al_0.3Ga_0.2P spacer layers to compensate the compressive strain of the InP QD layers, the CL and morphology are significantly improved. Using this technique, 30-stacked InP/In_0.5Al_0.3Ga_0.2P QD structures with improved CL properties and surface morphology were realized.     

Waveguiding Effect in Electroabsorption Modulators: Passivation Layers and Their Impact on Extinction Ratios

Waveguide structures of the stand‐alone electroabsorption (EA) modulator and the electroabsorption modulated laser (EML) are investigated using the 3D beam propagation method. The EA waveguide structures with InP‐based passivation layers show saturation in the extinction ratio (ER) due to the stray light traveling through the passivation layers. This paper demonstrates that narrower passivation layers suppress stray‐light excitation in the EA waveguide, increasing the ER. A taper structure in the isolation section of the EML waveguide can reduce the mode mismatch and suppress the excitation of the stray light, increasing the ER further. Low‐index‐polymer passivation layers can confine the mode more tightly in the active waveguide, yielding an even higher ER.     

Scanning force microscopy studies of GaAs films grown on offcut Ge substrates

The surface morphology of GaAs films grown on offcut Ge substrates is studied using a scanning force microscope (SFM). We investigated the effects of the Ge buffer layer, growth temperature, film thickness, and prelayer on the GaAs surface morphology. The starting Ge substrates are offcut 6° toward the [110] direction to minimize single steps on the substrates before molecular beam epitaxial film growth. We find that comparing with GaAs samples grown without Ge buffer layers or with unannealed Ge buffer layers, samples with annealed Ge buffer layers are much smoother and contain no antiphase boundaries (APBs) on the surface. For thick (≥1 μm) GaAs films with an annealed Ge buffer layer, the surfaces display crosshatch lines and elongated mounds (along , which are associated with the substrate offcut direction. As the film thickness increases, the crosshatch lines become shorter, denser and rougher, and the mounds grow bigger (an indication of GaAs homoepitaxial growth). We conclude that annealed Ge buffer layers are crucial for growing high quality GaAs films with few APBs generated during the growth. In addition, under optimal conditions, different prelayers make little difference for thick GaAs films with annealed Ge buffer layers.