p型InGaN/GaN超晶格N面GaN基LED的光电特性

随着氮(N)面GaN材料生长技术的发展,基于N面GaN衬底的高亮度发光二极管(LED)的研究具有重要的科学意义.研究了具有高发光功率的N面GaN基蓝光LED的新型结构设计,通过在N面LED的电子阻挡层和多量子阱有源层之间插入p型InGaN/GaN超晶格来提高有源层中的载流子注入效率.为了对比N面GaN基LED优异的器件性能,同时设计了具有相同结构的Ga面LED.通过对两种LED结构的电致发光特性、有源层中能带图、电场和载流子浓度分布进行比较可以发现,N面LED在输出功率和载流子注入效率上比Ga面LED有明显的提升,从而表明N面GaN基LED具有潜在的应用前景.     

Molecular‐Scale Hybridization of Clay Monolayers and Conducting Polymer for Thin‐Film Supercapacitors

Development of electrode materials with well‐defined architectures is a fruitful and profitable approach for achieving highly‐efficient energy storage systems. A molecular‐scale hybrid system is presented based on the self‐assembly of CoNi‐layered double hydroxide (CoNi‐LDH) monolayers and the conducting polymer (poly(3,4‐ethylene dioxythiophene):poly(styrene sulfonate), denoted as PEDOT:PSS) into an alternating‐layer superlattice. Owing to the homogeneous interface and intimate interaction, the resulting CoNi‐LDH/PEDOT:PSS hybrid materials possess a simultaneous enhancement in ion and charge‐carrier transport and exhibit improved capacitive properties with a high specific capacitance (960 F g^–1 at 2 A g^–1) and excellent rate capability (83.7% retention at 30 A g^–1). In addition, an in‐plane supercapacitor device with an interdigital design is fabricated based on a CoNi‐LDH/PEDOT:PSS thin film, delivering a significantly enhanced energy and power output (an energy density of 46.1 Wh kg^–1 at 11.9 kW kg^–1). Its application in miniaturized devices is further demonstrated by successfully driving a photodetector. These characteristics demonstrate that the molecular‐scale assembly of LDH monolayers and the conducting polymer is promising for energy storage and conversion applications in miniaturized electronics.     

Development of novel thermoelectric materials by reduction of lattice thermal conductivity

Thermal conductivity is one of the key parameters in the figure of merit of thermoelectric materials. Over the past decade, most progress in thermoelectric materials has been made by reducing their thermal conductivity while preserving their electrical properties. The phonon scattering mechanisms involved in these strategies are reviewed here and divided into three groups, including (i) disorder or distortion of unit cells, (ii) resonant scattering by localized rattling atoms and (iii) interface scattering. In addition, we propose construction of a ‘natural superlattice’ in thermoelectric materials by intercalating an MX layer into the van der Waals gap of a layered TX₂ structure which has a general formula of (MX)_1+x(TX₂)_n (M=Pb, Bi, Sn, Sb or a rare earth element; T=Ti, V, Cr, Nb or Ta; X=S or Se and n=1, 2, 3). We demonstrate that one of the intercalation compounds (SnS)_1.2(TiS₂)₂ has better thermoelectric properties compared with pure TiS₂ in the direction parallel to the layers, as the electron mobility is maintained while the phonon transport is significantly suppressed owing to the reduction in the transverse phonon velocities.     

InAs/GaSb超晶格红外探测器台面湿法腐蚀研究

研究了不同腐蚀体系对InAs/GaSb超晶格材料台面的刻蚀,并从中选择了由氢氟酸、酒石酸和双氧水构成的酒石酸腐蚀体系。该体系较适合InAs/GaSb超晶格材料的刻蚀,刻蚀速率稳定,下切效应小。进一步研究发现当HF达到一定浓度后不再影响刻蚀速度;在较低的酒石酸和双氧水浓度下,刻蚀速度是由氧化过程控制,且反应速度和双氧水的浓度成正比。腐蚀液配比为酒石酸(3.5g)∶H2O2(4mL)∶HF(1mL)∶H2O(400mL),刻蚀速度约为0.5μm/min。     

超晶格量子阱光学双稳态系统的全局分叉与混沌行为

基于超晶格量子阱的双稳态效应,在经典力学框架内,把粒子的运动方程化为了具有阻尼项和受迫项的摆方程.利用Melnikov方法分析了系统的全局分叉与Smale马蹄变换意义上的混沌行为,给出了系统通过级联分叉进入混沌的临界值.结果表明,系统进入混沌的临界条件与它的参数有关,只需适当调节这些参数就可以避免或控制混沌,为光学双稳态器件的设计提供了理论分析.     

Microstructure and stress corrosion cracking of the fusion boundary region in an alloy 182-A533B low alloy steel dissimilar weld joint

Stress corrosion cracking (SCC) in the fusion boundary (FB) region of an Alloy 182-A533B low alloy steel (LAS) dissimilar weld joint in high temperature water doped with sulfate was studied following a microstructure characterization of the FB region. The microstructure characterization suggested the type-II and type-I boundaries in the dilution zone (DZ) adjacent to the FB had lower resistance to SCC growth than the FB. Crack propagating perpendicular to the FB in the DZ was observed to be blunted by pitting at the FB, followed by the reactivation from the pitting by localized oxidation along the grain boundary in LAS.     

离子型声子晶体中的长波光学性质

提出了离子型声子晶体的概念，制备出一维离子型声子晶体材料，研究了一维离子型声子晶体中的超晶格振动与电磁波的耦合效应，将黄昆方程所预言的一系列长波光学行为，如：极化激元、红外吸收、介导异常等。从红外波段推广到微波波段，并得到了实验验证，预测了这种材料在微波与声学方面可能的应用。     

nBn型InAs/GaSb Ⅱ类超晶格红外探测器光电特性研究

设计了nBn结构的InAs/GaSb II类超晶格红外探测器,从理论和实验两方面对nBn器件的暗电流特性进行了研究,研究结果表明:理论计算的暗电流和实际测试结果趋势一致。另外,研制了p-i-n结构器件并与nBn器件进行了比较,测试结果显示:在77 K温度下,nBn器件的暗电流要比p-i-n器件暗电流小2个量级。温度升高到150 K时,nBn器件暗电流变大2个量级,而p-i-n器件暗电流变大4个量级;nBn器件峰值探测率下降到1/5,p-i-n器件峰值探测率下降2个量级。可见nBn器件适合高温工作,适合高性能红外焦平面探测器的研制。