Pt/Au/n-InGaN肖特基接触的电流输运机理

基于热电子发射和热电子场发射模式,利用I-V方法研究了Pt/Au/n-InGaN肖特基接触的势垒特性和电流输运机理,结果表明,在不同背景载流子浓度下,Pt/Au/n-InGaN肖特基势垒特性差异明显.研究发现,较低生长温度制备的InGaN中存在的高密度施主态氮空位（V_N）缺陷导致背景载流子浓度增高,同时通过热电子发射模式拟合得到高背景载流子浓度的InGaN肖特基势垒高度和理想因子与热电子场发射模式下的结果差别很大,表明V_N缺陷诱发了隧穿机理并降低了肖特基势垒高度,相应的隧穿电流显著增大了肖特基势垒总的输运电流,证实热电子发射和缺陷辅助的隧穿机理共同构成了肖特基势垒的电流输运机理.低背景载流子浓度的InGaN肖特基势垒在热电子发射和热电子场发射模式下拟合的结果接近一致,表明热电子发射是其主导的电流输运机理.     

InAs量子点在肖特基势垒二极管输运特性中的影响

在77到292K的范围内,系统研究了含InAs自组装量子点的金属-半导体-金属双肖特基势垒二极管的输运特性.随着温度上升,量子点的存储效应引起的电流回路逐渐减小.在测试温度范围内,通过量子点的共振隧穿过程在电流电压(I-V)曲线中造成台阶结构,且使电流回路随温度的上升急剧减小.根据肖特基势垒的反向I-V曲线,计算了势垒的反向饱和电流密度和平均理想因子.发现共振随穿效应使肖特基势垒在更大的程度上偏离了理想情况,而量子点的电子存储效应主要改变了肖特基势垒的有效势垒高度,从而影响了势垒的反向饱和电流密度 关键词： 自组装量子点 肖特基势垒 电流-电压特性     

SOI基高响应度TFET探测器的设计与仿真

提出一种SOI基的新型隧穿场效应晶体管(TFET)探测器结构,将光电二极管与TFET结合,实现光信号的探测放大。光电二极管的正极与TFET的栅极互连,感光后光电二极管的光生电势调控TFET的沟道势垒,控制TFET的输出电流,实现光信号到电流信号的转化。陡峭的亚阈值摆幅能有效放大输出电流,提高TFET探测器的响应度。应用SILVACO完成探测器结构和性能的模拟仿真。光电二极管的光生电势通过较薄的BOX区形成了TFET的底部栅压,增强了对沟道势垒的控制能力,增大了输出电流,结果表明,探测器对弱光具有较高的响应度,当入射光强小于10mW/cm~2时,响应度可超过10~4 A/W。此外,通过调整光电二极管的反偏电压、在源区与沟道间插入n~+口袋等方法可显著提高探测器的输出电流和响应度。     

双势垒磁性隧道结的磁电阻效应及其在自旋晶体管中的应用

利用磁控溅射方法沉积双势垒磁性隧道结多层膜, 其中Al-O势垒层由等离子体氧化1 nm厚的 金属铝膜方式制备，然后采用深紫外光曝光和Ar离子刻蚀技术、微加工制备出长短轴分别为 6和3 μm大小的椭圆形双势垒磁性隧道结（DBMTJ），并在室温和低温下对其自旋电子输运 特性进行了研究. DBMTJ的隧穿磁电阻(TMR)比值在室温和42 K分别达到27％和423％， 结电阻分别为136 kΩ·μm²和175 kΩ·μm²，并在实验中观 察到平行状 态下存在低电阻态及共振隧穿效应，反平行态下呈现高电阻态以及TMR随外加偏压或直流电 流的增加而发生振荡现象. 由此，设计了一种基于这种双势垒磁性隧道结隧穿特性的自旋晶 体管. 关键词： 双势垒磁性隧道结 隧穿磁电阻 共振隧穿效应 自旋晶体管     

超薄栅氧化层n-MOSFET软击穿后的导电机制

研究了恒压应力下超薄栅氧化层n型金属-氧化物-半导体场效应晶体管（n-MOSFET）软击穿 后的导电机制.发现在一定的栅电压V_g范围内，软击穿后的栅电流I_g符合Fowl er-Nordheim隧穿公式，但室温下隧穿势垒_b的平均值仅为0936eV，远小于S i/Si O₂界面的势垒高度315eV.研究表明，软击穿后，处于Si/SiO₂界 面量子化能级上的 电子不隧穿到氧化层的导带，而是隧穿到氧化层内的缺陷带上._b与缺陷带能 级和电 子所处的量子能级相关；高温下，激发态电子对隧穿电流贡献的增大导致_b逐 渐降低. 关键词： 软击穿 栅电流 类Fowler-Nordheim隧穿 超薄栅氧化层     

基于4H-SiC肖特基势垒二极管的γ射线探测器

针对极端环境下耐高温和耐辐照半导体核探测器的研制需求,采用外延层厚度为100μm的4H碳化硅(4H-SiC)制备成肖特基二极管探测器,研究了该探测器对~(241)Am源γ射线的能谱响应.采用磁控溅射金属Ni制备了肖特基二极管的欧姆接触和肖特基接触,利用室温电流-电压和电容-电压测试研究了二极管的电学特性.欧姆特性测试表明,1050°C退火时,欧姆接触特性最好.从正向电流-电压曲线得出二极管肖特基势垒高度为1.617 eV,理想因子为1.127,表明探测器具备良好的热电子发射特性.从电容-电压曲线获得二极管外延层净掺杂浓度为2.903×10~(14)cm~(-3),并研究了自由载流子浓度在外延层中的纵向分布.在反向偏压为500 V时,二极管的漏电流只有2.11 nA,具有较高的击穿电压.测得在-300 V条件下,SiC二极管探测器对能量为59.5 keV的γ射线的能量分辨率为9.49%(5.65 keV).     

半导体量子器件物理讲座第四讲 共振隧穿器件及其电路应用

当一个电子的能量低于势垒高度时,它仍可以隧穿通过势垒,在一定条件下,双势垒结构中电子的隧穿几率甚至可以接近1,利用这种共振隧穿现象可以做成共振隧穿二极管,它的电流－电压特性曲线中会出现负微分电阻,利用这种负阻效应可以做成高频振荡器和倍频器等电子器件,双势垒结构与通常的双极晶体管结合可以做成共振隧穿双极晶体管,它们可以用来做成多态记忆器和模数转换器等器件。     

基于两步退火法提升Al/n~+Ge欧姆接触及Ge n~+/p结二极管性能

锗(Ge)中高激活浓度、低扩散深度的n型掺杂是实现高性能Ge n-MOSFET的重要前提条件.本文采用低温预退火与脉冲激光退火相结合的两步退火法,结合磷离子注入,制备Al/n~+Ge的欧姆接触以及Ge n~+/p结二极管.通过电流-电压特性测试来研究Al/n~+Ge的欧姆接触以及Ge n~+/p结二极管的性能,测试结果表明:低温预退火可初步修复注入损伤,并降低激光退火时杂质的扩散深度;结合离子注入工艺和两步退火工艺,Al/n~+Ge欧姆接触的比接触电阻率降至2.61×10~(-6)Ω·cm~2,Ge n~+/p结二极管在±1V的整流比提高到8.35×10~6,欧姆接触及二极管性能均得到了显著提升.     

处理具有任意形状势垒的磁性隧道结中电子输运的一个简单方法

在Slonczewski自由电子模型的基础上,提出了一个可用于处理具有任意形状势垒的磁性隧道结中磁电子输运的简单方法,并以三种常见构形的势垒,即梯形势垒,计入了镜像势的梯形势垒和抛物线势垒为例,讨论了势垒形状对隧穿磁电阻及其随偏压变化的影响. 关键词： 磁性隧道结 隧穿磁电阻 任意形状势垒 非零偏压     

低反向漏电自支撑衬底AlGaN/GaN肖特基二极管

氮化镓材料具有大的禁带宽度(3.4 eV)、高的击穿场强(3.3 MV/cm),在高温、高压等方面有良好的应用前景.尤其是对于铝镓氮/氮化镓异质结构材料而言,由极化效应产生的高面密度和高迁移率二维电子气在降低器件导通电阻、提高器件工作效率方面具有极大的优势.由于缺乏高质量、大尺寸的氮化镓单晶衬底,常规氮化镓材料均是在蓝宝石、硅和碳化硅等异质衬底上外延而成.较大的晶格失配和热失配导致异质外延过程中产生密度高达10~7—10¹⁰ cm^–2的穿透位错,使器件性能难以进一步提升.本文采用基于自支撑氮化镓衬底的铝镓氮/氮化镓异质结构材料制备凹槽阳极结构肖特基势垒二极管,通过对欧姆接触区域铝镓氮势垒层刻蚀深度的精确控制,依托单步自对准凹槽欧姆接触技术解决了低位错密度自支撑氮化镓材料的低阻欧姆接触技术难题,实现了接触电阻仅为0.37Ω·mm的低阻欧姆接触;通过采用慢速低损伤刻蚀技术制备阳极凹槽区域,使器件阳极金属与氮化镓导电沟道直接接触,实现了高达3×107开关比的高性能器件,且器件开启电压仅为0.67 V, 425 K高温下,器件反向漏电仅为1.6×10...     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.