GaN/GaAlN宽量子阱的二类激子特征

考虑了内建电场的影响,用变分法计算了GaN/GaAlN量子阱(QW)的电子子带和激子结合能.结果表明,对于阱宽较大情形,电子和空穴高度局域在QW边沿附近.内建电场造成的电子空穴空间的较大分离使QW激子表现出二类阱特征.重空穴基态结合能对Al浓度变化不敏感.     

流体静压力下应变闪锌矿(111)取向GaN/AlGaN量子阱中受屏蔽激子的结合能

结合变分法与自洽计算方法研究了流体静压力下应变闪锌矿(111)取向GaN/AlχGa1-χN量子阱中受电子-空穴气体屏蔽的激子结合能.计算中,考虑了沿(111)取向生长多层结构时存在压电极化引起的内建电场.计算结果表明,考虑压力对双轴及单轴应变的调制以及禁带宽度、有效质量和介电常数等参数的压力效应时,激子结合能随压力的增大近似线性增加;且当电子-空穴气体密度大时,这一效应更加显著.当给定压力时,随着电子.空穴气面密度的增加,激子结合能先缓慢增加,但当密度达到大约1011cm-2时结合能开始迅速衰减.此外,当减小垒的厚度时,由于内建电场减弱,激子结合能显著增加.     

流体静压力下应变闪锌矿(111)取向GaN/AlGaN量子阱中受屏蔽激子的结合能

结合变分法与自洽计算方法研究了流体静压力下应变闪锌矿(111)取向GaN/AlχGa1-χN量子阱中受电子-空穴气体屏蔽的激子结合能.计算中,考虑了沿(111)取向生长多层结构时存在压电极化引起的内建电场.计算结果表明,考虑压力对双轴及单轴应变的调制以及禁带宽度、有效质量和介电常数等参数的压力效应时,激子结合能随压力的增大近似线性增加;且当电子-空穴气体密度大时,这一效应更加显著.当给定压力时,随着电子.空穴气面密度的增加,激子结合能先缓慢增加,但当密度达到大约1011cm-2时结合能开始迅速衰减.此外,当减小垒的厚度时,由于内建电场减弱,激子结合能显著增加.     

GaN基量子阱激子结合能和激子光跃迁强度

采用变分法,计算了GaN基量子阱中激子结合能和激子光跃选强度。计算结果表明,GaN基量子阱中激子结合能为10－55meV,大于体材料中激子结合能,并随着阱宽减小而增加,在临界阱宽处达到最大。结间带阶同样对激子结合能有着较大的影响,更大带阶对应更大的结合能。同时量子限制效应增加了电子空穴波函数空间重叠,因此加强了激子光跃迁振子强度,导致GaN/AlN量子阱中激子光吸收明显强于体材料中激子光吸收。     

耦合ZnO/MgxZn1-xO量子点中的激子态和带间光跃迁

在有效质量近似和变分原理的基础上,考虑量子点的三维约束效应和内建电场.研究了ZnO/MgxZn1-xO0耦合量子点中激子结合能、带间光跃迁能以及电子-空穴复合率随量子点结构参数(量子点高度和势垒层厚度)的变化.结果表明:激子结合能、带间光跃迁能和电子-空穴复合率随量子点高度或势垒层厚度的增加而降低.     

Al含量对GaN/AlxGa1－xN量子点中激子态的影响

利用有效质量方法和变分原理，考虑内建电场和量子点的三维约束效应，研究了Al含量对局域在GaN/AlxGa1－xN量子点中激子性质的影响．结果表明，随着Al含量的增加，GaN/AlxGa1－xN异质界面处的导带不连续性增强，势垒变高，载流子受到的约束增强，激子结合能增加，电子空穴的复合率先增大后减小，且存在最大值．对给定体积的量子点，随其高度的变化激子结合能存在最大值，相应的电子空穴被最有效约束，激子态最稳定．     

势阱形状对电场下量子阱子带和激子能移的影响

在束缚态近似下,用级数解法求解电场下各种不同形状GaAs/GaAlAs量子阱中电子和空穴子带,进一步采用变分方法得到激子结合能.由此,我们首次得到电场下由抛物阱至方位阱子带和激子峰能移的变化图象.在考虑GaAs/GaAlAs量子阱形状影响的基础上,我们计算所得结果与实验吻合得很好.     

外场对InPBi量子阱中激子结合能的影响

在有效质量近似下运用变分法计算了InAlAs/InPBi/InAlAs量子阱中的激子结合能随阱宽、Al组分、Bi组分的变化情况,分析了外加电场和磁场对激子结合能的影响。结果表明：激子结合能随阱宽增大呈现先增大后减小的趋势;随Al、Bi组分的增大,激子结合能也逐渐增大;外加电场较小时对激子结合能的影响很小,外加电场较大时破坏了激子效应;激子结合能随外加磁场增大呈现单调增大的趋势。计算结果对InAlAs/InPBi/InAlAs量子阱在光电子器件方面的应用有一定指导意义。     

纤锌矿GaN/AlxGa1-xN量子阱中激子能量

考虑了纤锌矿GaN/Al<,x>Ga<,1-x>N量子阱(QW)材料中空穴带质量和光学声子模的各向异性以及声子频率随波矢变化的效应,采用改进的LLP变分法计算了纤锌矿氮化物QW中激子的基态能量和结合能.给出了激子的基态能量和结合能随着QW宽度和Al组分变化的函数关系,并对闪锌矿和纤锌矿GaN/Al<0.3>Ga<,0....     

Al含量对GaN/Alx Ga1-x N量子点中激子态的影响

利用有效质量方法和变分原理,考虑内建电场和量子点的三维约束效应,研究了Al含量对局域在GaN/AlxGa1xN量子点中激子性质的影响.结果表明,随着Al含量的增加,GaN/AlxGa1-xN异质界面处的导带不连续性增强,势垒变高,载流子受到的约束增强,激子结合能增加,电子-空穴的复合率先增大后减小,且存在最大值.对给定体积的量子点,随其高度的变化激子结合能存在最大值,相应的电子-空穴被最有效约束,激子态最稳定.     

聚对苯撑苯并双(口恶)唑发光及其器件制备

采用光谱技术,研究了聚对苯撑苯并双(口恶)唑(PBO)溶液的光敏发光特性,并用相对法估算出溶液发光效率在50%范围.结合光谱技术、半导体电学和电化学等研究手段,具体研究了以PBO为发光层的单层电致发光器件,研究结果显示,电致发光与薄膜的光致发光有具有相同的发光中心,峰值位于510 nm左右.同时发现,由于存制备过程中不同处理条件使得不同厚度薄膜残留的掺杂物质浓度不同,从而引起薄膜的导电性的不同.使得器件的阈值场强随PBO厚度的减小而逐渐增加.     

系统级封装新型埋入式电源滤波结构的研究

在高密度小尺寸的系统级封装(SiP)中,对供电系统的完整性要求越来越高,多芯片共用一个电源网路所产生的电压抖动除了会影响到芯片的正常工作,还会通过供电网路干扰到临近电路和其他敏感电路,导致芯片误动作,以及信号完整性和其他电磁干扰问题.这种电压抖动所占频带相当宽,几百MHz到几个GHz的中频电源噪声普通方法很难去除.结合埋入式电容和电源分割方法的特点,提出一种新型高性能埋入式电源低通滤波结构直接替代电源/地平面.研究表明,在0.65～4GHz的频带内隔离深度可达-40～75 dB,电源阻抗均在0.25ohm以下,实现了宽频高隔离度的高性能滤波作用.分别用电磁场和广义传输线两种仿真器模拟,高频等效电路模型分析这种低通滤波器的工作原理以及结构对隔离性能的影响,并进行了实验验证.     

Emerging interconnects: a state-of-the-art review and emerging solutions

Aluminium was a primary material for interconnection in integrated circuits (ICs) since their inception. Later, copper was introduced as interconnect material which has better metallic conductivity and resistance to electromigration. As the aggressive technology scaling continues, the copper resistivity increased because of size effects, which causes increase in delay, power dissipation and electromigration. The need to reduce the resistor-capacitor??????? delay, dynamic power utilisation and the crosstalk commotion is as of now the fundamental main impetus behind the presentation of new materials. The purpose of this paper is to do a survey of interconnect material used in IC from introduction of ICs to till date. This paper studies and reviews new materials available for interconnect application which are optical interconnects, carbon nanotube (CNT), graphene nanoribbons (GNRs) and silicon nanowires which are alternatives to copper. While doing a survey of interconnect material, it is found that multiwalled CNTs, multilayer GNR and mixed CNT bundles are promising candidates and are ultimate choice that can strongly address the problems faced by copper but on integration basis copper would last for coming years.     

Arsenic deposition as a precursor layer on silicon (211) and (311) surfaces

We investigate the properties of arsenic (As) covered Si(211) and Si(311) surfaces by analyzing data from x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) images. We then create a model using total surface energy calculations. It was found that both Si(211) and Si(311) had 0.68±0.08 surface As coverage. Si(211) had 0.28±0.04 Te coverage and Si(311) had 0.24±0.04 Te coverage. The Si(211) surface replaces the terrace and trench Si atoms with As for a lower surface energy, while the Si edge atoms form dimers. The Si(311) surface replaces all terrace atoms and adsorbs an As dimer every other edge site. These configurations imply an improvement in the mean migration path from the bare silicon surface by allowing the impinging atoms for the next epitaxial layer, tellurium (Te), to bind at every other pair of edge atoms, and not the step terrace sites. This would ensure a nonpolar, B-face growth.     

光子晶体微腔发光二极管

光子晶体微腔因其具有增强自发辐射、定向输出和单模工作的能力而受到广泛关注。介绍了光子晶体微腔发光二极管的基本原理、设计、特性、制作及其典型器件。     

用于单光子TOF测量的时间-幅度变换器

基于新型共源共栅电流源的积分方法,设计了一种用于单光子飞行时间(TOF)测量的时间-幅度变换器(TAC)。该方法有效简化了TAC电路结构,减小了TAC占用面积,显著提高了TOF的满量程范围(FSR)。采用0.18 μm标准CMOS工艺设计。集成TAC的单光子探测器像素单元的填充因子可达到26.8%。后仿真结果表明,该TAC在120 ns的FSR内具有230 ps的定时分辨率,微分非线性(DNL)低于0.05 LSB,积分非线性(INL)低于1.1 LSB。蒙特卡洛仿真表明,512个TAC像素间的不均匀性低于0.5 %。该TAC非常适用于高密度时间相关的单光子计数(TCSPC)探测器阵列。     

Comparative study of maximum power point tracking techniques for hybrid renewable energy system

The power generation demand is increasing day-by-day throughout the world, therefore, the use of hybrid systems becomes a significant solution. The hybrid renewable energy system (HRES) is used for delivering power in various regions in order to overcome intermittence of wind and solar resources. Because of increasing environmental problems, for example, greenhouse gas emission and energy cost have interested novel research into substitute methods in favour of electrical power generation. Maximum Power Point Tracking (MPPT) control method is a vast deal of novel research used for enhancing the efficiency of HRES. The authors have revealed that the hybrid techniques i.e. Global MPPT, fuzzy-neuro systems, Adaptive Neuro-Fuzzy Inference System (ANFIS), Perturbed and Observe (P&O) + Adaptive Neural Network (ANN) etc. can provide best results as compared to other MPPT control methods. This paper offering a state of art review of MPPT control techniques for HRES.     

Joint estimation of TOA and DOA in IR-UWB system using a successive propagator method

Impulse radio ultra-wideband (IR-UWB) ranging and positioning require accurate estimation of time-of-arrival (TOA) and direction-of-arrival (DOA). With receiver of two antennas, both of the TOA and DOA parameters can be estimated via two-dimensional (2D) propagator method (PM), in which the 2D spectral peak searching, however, renders much higher computational complexity. This paper proposes a successive PM algorithm for joint TOA and DOA estimation in IR-UWB system to avoid 2D spectral peak searching. The proposed algorithm firstly gets the initial TOA estimates in the two antennas from the propagation matrix, then utilises successively one-dimensional (1D) local searches to achieve the estimation of TOAs in the two antennas, and finally obtains the DOA estimates via the difference in the TOAs between the two antennas. The proposed algorithm, which only requires 1D local searches, can avoid the high computational cost in 2D-PM algorithm. Furthermore, the proposed algorithm can obtain automatically paired parameters and has better joint TOA and DOA estimation performance than conventional PM algorithm, estimation of signal parameters via rotational invariance techniques algorithm and matrix pencil algorithm. Meanwhile, it has very close parameter estimation to that of 2D-PM algorithm. We have also derived the mean square error of TOA and DOA estimation of the proposed algorithm and the Cramer-Rao bound of TOA and DOA estimation in this paper. The simulation results verify the usefulness of the proposed algorithm.     

超宽带脉冲信号的光学生成方法研究

近年来超宽带(UWB)通信技术迅猛发展,在测量、雷达技术、民用和军事无线通信中有着重要的应用,UWB-over-fiber技术已经成为目前研究的热点,其中就包括UWB脉冲信号的产生方法。区别于传统的电子学方法,光子学产生方法不受电子瓶颈制约,可以实现很高的带宽,并且具有抗电磁干扰、重量轻、结构紧凑的优点。通过对比国内外本领域研究成果,讨论及总结了以下三种原理的UWB脉冲信号的光学生成方法:1)相位调制-强度调制转换(PM-IM);2)半导体光放大器(SOA)的非线性效应;3)频谱塑形和色散所致频域-时域映射,然后对各种方案进行了对比分析。     

多孔硅发光机制的分析

从量子力学的基本理论出发讨论了量子限制效应，推导出多孔硅有效禁带宽度增量并用量子限制效应和表面态及其物质在发光中作用的理论解释了ＰＳ光致发光的实验现象。